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We are saddened to announce the passing of Gary Bunzer on April 17, 2020. We hope the RV Doctor website will continue to provide helpful information for you. Thank you for your interest and support for the RV Doctor - Debbie, Heather and Gretchen

Sunday, January 7, 2001

Recreation Vehicle Waste Management Practices

By Gary Bunzer

Gather any two or three RV owners together and engage them in a discussion of RV plumbing systems and invariably, the discourse will eventually turn to one of the most displeasing, yet necessary aspects of RVing; that of waste containment, evacuation and sanitation. The proverbial dumping of the holding tanks, often considered a necessary evil and a relatively simple process, can, in some cases, cause more consternation (and operational problems), than one might fully understand. As disagreeable a chore as it may be, given the technology available today, plus heightened environmental awareness, there is a renewed vigor to properly store, evacuate and maintain the waste plumbing systems on all RVs!

There have been some interesting advancements in products and processes in many areas of waste plumbing, so with disposable gloves in hand, let’s spend a little time investigating improved waste management practices and learn about a few products that just may allow us to lessen our burden of it.

Always take extra precaution when working on RV waste plumbing systems; even when simply evacuating the holding tanks. Always wear disposable gloves when handling sewer hoses and
connections. Many coach owners have installed a glove and disinfectant dispenser
right in the waste plumbing bay as a reminder.

When using hand tools while working on the waste systems, be sure to clean and disinfect
 them after each use. Those same tools may be working on the fresh water system next!
A can of spray disinfectant is also a handy item to carry with you as you travel.

Black and Gray
A common mindset is to separate, (at least ideologically), RV waste plumbing into two separate waste systems; the gray system (liquid waste) and the black system (solid waste). However, in some cases, due primarily to the design of the floor plan, it is plausible to find some coaches having at least one liquid fixture drain into the black holding tank. In my opinion, this is not an optimum situation. It may necessitate more frequent tank evacuations, which could become an additional burden for those who prefer dry camping, but it is certainly permissible by code. Ah, but the discourse you are reading is not limited simply to the holding tanks. From my perspective, once fresh water leaves any faucet and showerhead or enters the toilet, it becomes waste water. So begins our management of it. 

Odor Control
One of the most common complaints of RVers is the proliferation of obnoxious odors emanating from the waste plumbing system. Nothing can ruin an excursion faster than having holding tank odors permeate the interior of the coach. The first line of defense against invading fumes is the water lock established by P-traps located below the sinks and tub/shower drains. 
Long a staple in the plumbing trades, the common P-trap has served us well for many years. There is a downside however, especially concerning recreation vehicle P-traps that are used less frequently than commercial or residential applications. Oftentimes the water seal in a coach P-trap is diminished or lost altogether. The jostling that occurs while traveling, improper siphoning action during highway turns and tank evacuations or simply drying out from non-use can render the water seal ineffective at blocking holding tank odors from entering the living area of an RV. In addition, the P-trap requires diligent maintenance; frequent cleanings and freeze protection are necessary and often overlooked. If neglected, waste residue inside the traps can foster bacteria growth and subsequent odors from within.

Enter a new product, the HepvO waterless sanitary valve. Available in the aftermarket and now found on many coaches right from the factory, the HepvO waterless valve replaces the common P-trap, thereby creating an effective seal against odors while providing additional storage space (who reading this would not appreciate having more room for personal effects?).

This ingenious sanitary valve is constructed with a self-sealing, yet flexible, silicone-derived membrane that allows water to flow through it, but completely closes off when water flow stops thereby preventing holding tank odors from migrating up and through the sinks and the tub or shower. The HepvO is also an effective air-admittance device, which eliminates the need for mandated anti-siphon trap vent devices at fixture P-trap arms; (more on ASTVDs later).

With no standing water as in a P-trap, the HepvO waterless valve eliminates the possibility of bacteria growth and eliminates the freeze concern and evaporation issues. Check out this RV Doc video!

As for the toilet, I probably do not have to remind everyone to always keep water in the bowl at all times, though that may become a challenge when the coach is stored for a lengthy period. Still, with water in the bowl, you are guaranteed that no holding tank odors can escape into the living areas of the coach.

If you find the toilet simply will not hold water endlessly, chances are it is time to replace all the internal seals and gaskets. You’d be surprised to see just how many seals are used in an RV toilet! Dried out toilet seals are the main sources of black tank odors permeating the interior of the coach. Most toilet manufacturers package gasket repair kits for their line of toilets. And unless you swap out toilets regularly, chances are this type of maintenance will be necessary at some point during your RVing career.

To verify the toilet water seal is not leaking, (or IS leaking!), simply place a light pencil mark in the bowl at the level of the water after a normal flushing process and observe it over time. As I state in my seminars, if water can seep past the seal, odors will eventually pass up from the holding tank.

Waste System Venting
Coach makers typically (or rather, should), rely on the NFPA 1192, Standard on Recreational Vehicles, as the guiding standard for how waste plumbing components are designed, listed and installed. The NFPA 1192, which is adopted and endorsed by RVIA, is edited every three years in order to keep up with new designs and technological improvements to better serve the entire RV industry.

Paragraphs and specifically address the area of holding tank venting. Venting is required for both the black and the gray system and the method chosen by most RV manufacturers is to run a length of ABS pipe from the holding tank, up and through the roof of the RV. The importance of proper venting, in both systems, cannot be overstated, especially as it relates to odor control. Additionally, without correct venting, sinks will not drain properly, bacteria can propagate and holding tanks will not drain as quickly or completely.

Keep in mind, as a holding tank empties or a sink drains, fresh air must enter the drainage system. Since RV fixtures as well as holding tanks rely solely on gravity for emptying, having air enter the system as sinks and tanks are drained, results in a faster and more thorough process. There are two types of vents used in recreation vehicle waste systems: direct exterior vents and the aforementioned anti-siphon trap vent devices (ASTVDs).

Direct Vents
Direct vents connect the waste systems (either within the drain piping or directly from the holding tank) to the atmosphere outside. As mentioned earlier, most coach manufacturers install a vertical section of plastic ABS piping up and through the roof of the coach for both the black and gray systems.

There is one other type of direct vent; a side-mounted vent. Side venting is only permissible in the liquid waste system, (typically from a single fixture), and only found on the smallest recreation vehicles. Clearly, the most common and the most effective waste system vents, however, are those that protrude above the roof.

Anti-Siphon Trap Vent Devices (ASTVD)
Another type of vent is the anti-siphon trap vent device. These handy gadgets are used as a secondary vent to aid in draining sink fixtures. Also called “check vents,” ASTVDs allow air into the drainage system, but prohibit air from passing out of the system. ASTVDs are installed in the liquid drain piping system, at or near a P-trap inside a cabinet. Look under the kitchen and lavatory sink area and you should find them. They are mounted at least 6-inches above the P-trap’s horizontal arm. ASTVDs do not allow odors to escape into the living portion of the RV because of an integral atmospheric pressure-controlled, rubberized, one-way valve. In other words, air in, but not out.

In addition to ASTVDs, there must still be at least one vent protruding through the roof to allow sewer gases out of that holding tank; ASTVDs are not primary vents. The better-designed waste systems will have ASTVDs installed at every P-trap as well as a direct vent running from each holding tank up and through the roof. Remember though, with the advent of the HepvO waterless sanitary valve, ASTVDs are not required. With the HepvO, eliminating the ASTVD and the P-trap should result in more cubic inches of storage space under every sink. During manufacture, coach makers can eliminate the cost of P-traps, ASTVDs (and their associated fittings, tee’s and piping), as well as shower-mounted skylights, besides gaining the extra storage space.

Direct Vent Maintenance
If I were a betting man, I’d wager not many active RVers have ever given serious thought to actually performing any maintenance on the waste system vents. But here’s something to investigate if you’ve never done so before. Sometimes coach manufacturers cut a very large hole in the ceiling and roof for vertical vent pipes to pass through; it obviously makes the installation a little easier and a lot faster. Oftentimes this opening is not sealed properly all the way around the outside perimeter of the pipe. In other instances, the vent pipe itself may not extend far enough above the roofline. According to the NFPA 1192, “each vent pipe shall pass through the roof and terminate vertically, undiminished in size, not less than 2-inces above the roof.”

Any scenario consisting of a short vent pipe (less than 2-inches above the roof), the area around the pipe not sealed properly and routed through an oversized hole, is likely to have tank odors pass up the vent, collide with the underside of the sewer vent cap and be forced back down, around the side of the vent pipe and into the ceiling area where it eventually migrates to the living area and you inhale the results.

It would behoove the serious coach owner to remove the top cap of each sewer vent on the roof and ensure the space around the vent pipe is sealed tight, and that the pipe itself stands at least two inches above the roof. If necessary, extend the vent by using a common ABS coupling and a short piece of pipe.

In addition, depending on how the vent is attached to the top of the holding tank, vent pipes have been known to fall down inside the tank below the surface of the waste, nullifying any venting action whatsoever and allowing tank odors to exit the open end of the vent virtually within the ceiling void or even inside an interior wall pocket. By inspecting the vent termination on the roof regularly, this can be avoided.

ASTVD Maintenance
The rubber membrane employed in ASTVDs can sometimes dry out and become stuck in the open position. If holding tank odors are prominent under a galley or lavatory cabinet near the P-trap, chances are it’s time to lubricate the rubber seal inside the ASTVD. Use Dow 111 lubricant to moisten the rubber diaphragm. Since it is located above the actual flow of waste water, the ASTVD is simply threaded into a fitting above the trap arm and is usually easily removed for inspection and periodic lubrication.

Anti-Odor Accessories
Though the NFPA 1192 mandates certain products and practices for the coach manufacturer, it does not require the inclusion of a cap on the direct vents protruding through the roof. Those makers that do install one at the factory, do so to keep objects and critters from entering the open end of the vent stack. But typical roof vent caps or covers are not intended or designed to control or aid in odor elimination.

It is quite common to see a couple of open-ended, 1-1/2-inch ABS vent pipes, uncapped on the roof of the RV. They will be sealed, however, by a flashing of some type to keep moisture out of the roof and ceiling areas, but open-ended vent pipes and even those covered by typical caps can actually create odor problems for the RVer. The dynamics of air flow, (side drafts, down drafts and up drafts), all create a higher atmospheric pressure inside the holding tanks, forcing odors to escape into the interior of the RV through dried out P-traps, empty toilet bowls, faulty anti-siphon trap vent devices, internal toilet hoses or any other air leak in the venting or drainage system.

But as you’ll often hear me state, thank goodness for the aftermarket! Today, a revolutionary roof vent cap is available to all RVers. 360 Products, Inc., produces a non-mechanical vent cap marketed as the 360 Siphon. Any RV owner can purchase the 360 Siphon online from Drainmaster.com. This unique vent assembly is designed to grab the slightest breeze and literally suck the fumes out of the holding tanks. Scientifically developed (every design feature has a function), it utilizes a combination of the Bernoulli Principle and the venturi effect, (of which I won’t bore you with the details here). The 360 Siphon successfully produces a negative pressure inside the holding tank and vent stack, thereby drawing odors out of the tank. It’s one of those “no-brainer” purchases that will enhance the lifestyle of every RVer.

Where would we be with out it? For one thing, up in the air I suppose! But it is a vital decree that coach makers must adhere to, along with anyone who repairs or modifies the waste plumbing system on the RV. The force behind any sink drain and holding tank evacuation is gravity and we all know liquids will not flow uphill. Without the proper slope, drainage can be slowed, plugged or otherwise negatively affected. If you have experienced improper drainage at any receptacle or holding tank, perhaps a close inspection of the slope of each drainpipe and holding tank termination assembly is in order.

According to NFPA 1192, Paragraph, horizontal runs of waste piping should slant towards the holding tank no less than 1/8-inch per linear foot. Additionally, the waste piping should be supported not less than every four feet. If allowed to sag, belly-down or slope upwards, waste water can be trapped inside the drain system and become a breeding ground for bacteria growth as well as odors.

Additionally, ABS plastic fittings used throughout the drainage system must be designed with an integral slope of 1/4-inch per foot. I have witnessed unknowing RV service technicians install elbows, tees and wyes not meant for RV waste systems even though the exterior design of the fitting looked correct. Typically, the built-in slope is molded into the internal portion of the fitting. This is not a problem as the coach leaves the factory, but can become problematic if plumbing repairs are performed by non-Certified technicians in the field.

Holding Tanks
If you own an RV, you know about holding tanks. What you may not know about holding tanks is that only the solid waste, black holding tank, is required to have a 3-inch outlet. Liquid waste tanks can be outfitted with a drain opening as small as 1-1/2-inch. A smaller outlet somewhat restricts the flow of the waste water as the tank is emptied. A slower, less forceful drainage flow will oftentimes not have enough velocity behind it to totally flush out the tank, the termination assembly and the sewer hose, which can result in the retention of waste residue. Any accumulation of waste, anywhere, can lead to odors. It should be obvious by now, that one of the intended purposes of this article is to eliminate or at least, minimize waste system odors, so hat’s off to those coach makers who utilize a full, 3-inch outlet on the gray tanks as well as the black holding tanks!

Tests have proven that faster dumping sequences will increase the flushing action resulting in all waste being quickly washed away rather than having it slowly recede down the tank walls and trickle through a smaller opening. This negative hydrophilic action is akin to observing buttermilk as it drips down the sides of a drinking glass.

Tank Additives
Another odor-related topic serious RVers should consider concerns holding tank additives. Much has been touted about which products work and don’t work, but the bottom line suggests using only environmentally-friendly additives that do more than simply mask the odor in the tanks and break down the solid waste. Enzyme-based, bacteria-infused holding tank additives have proven to be the most effective tank additive. Please note I said “additives,” and not chemicals. Enzyme-based blends actually digest the odor-causing molecules at the source inside the waste tanks, thereby eliminating odors rather than masking them. We’ve all smelled so-called additives that were almost as obnoxious as the tank odor itself, right?

Additionally, some holding tank treatments may consist of harmful chemicals such as formaldehydes, quaternary-based and phenol-based compounds. These are to be avoided. The issue of chemical products has prompted many state parks, campgrounds, dump stations and local municipalities to ban the evacuation of RV holding tanks if such chemicals are used.

RV holding tanks are living, thriving environments to a certain extent. And with the inclusion of an enzyme-based, live bacteria additive proliferating and percolating inside each holding tank, never use anti-bacterial soaps, detergents or home brews commonly discussed on Internet forums. Such use can destroy the “good bugs” that are more beneficial in helping the elimination of odors.

I’ve had good success with Pure Power Blue, produced by OP Products. I’ve had some field tests performed in hot summer and in different locations around the country. Pure Power Blue is the strongest additive I’ve found and it does a great job of breaking up the solids in the holding tanks. Take a look at my Product Spotlight video here.

Tank Monitoring
Most all RVs today feature some visual method of determining the levels in a variety of onboard containers such as the fresh water tank, both waste holding tanks, fuel tanks and the propane container. It’s a nice convenience to simply push a button inside the coach and know just how full the holding tanks are and when it is time to find a dump station, before a panic develops. Some holding tanks are equipped with “through the wall” monitoring sensors while others utilize externally applied, electronic sensors. It’s those “through the wall” sensors that aggravate anyone so equipped. False or inaccurate monitor panel indications caused by tank sludge and debris hanging up on the sensor probes inside the tank are far too common. That’s the bad news. The good news is that a revolutionary in-tank sensor for both the gray and black holding tanks has been developed by Horst Dynamics. These new probes are now available and easily installed by any RV handyperson once the original sensors are accessed.

Tank Blockages
The most dreaded line item on any RV service technician’s repair order is the one that states, “Black tank plugged; tank is full.” Nothing can ruin both a coach owner’s and a service technician’s day faster than having any type of blockage in a holding tank; and as you might have guessed, it happens predominantly with the black, solid waste holding tank.

Unfortunately, some holding tanks are constructed with an offset “shelf” built into its configuration in order to facilitate a specific floor plan. Most toilets are positioned directly over the black tank and it’s regrettable when the toilet empties into the tank right above this integral shelf. Mercifully, not many of the larger coaches suffer from this ill-advised design, but there are indeed a number of them out there. Which is why most RV service techs keep an extra uniform at the shop at all times.

The easiest way to avoid black tank blockages is to use copious amounts of fresh water during each flushing of solid waste. Those who flush out each holding tank completely after evacuation will likely avoid the dreaded holding tank blockage. Always be sure to always cover the very bottom of each holding tank with fresh water after each evacuation. And do not store the coach for lengthy periods with contents still in the tank. Dried out solids can quickly gather against the termination valve and in the smaller, more restricted, outlet of the tank.

Tank Terminations
All holding tanks, as you already know, are equipped with a full way termination valve installed somewhere downstream of the tank outlet and just prior to the termination assembly where the sewer hose is connected. The termination valve, tank valve, dump valve, slide valve, waste valve, blade valve, gate valve, whichever term you prefer to call it, is often improperly installed at the factory. For years it has been a common practice to install the valve(s) in a horizontal orientation whereby the body of the valve is positioned parallel to the ground. In some cases, I have even seen the valve slanted drastically downwards, (see photo). It is my opinion that manufacturers do this to allow for an easier pull on the T-handle when evacuating the tanks. In some cases, it’s to accommodate the installation of those dreaded cable and pull rods. A better, (read: optimum), installation should have the body of the valve straight up or at least slanted upwards. Here’s why.

The larger main housing of any termination valve is simply a void into which the blade can be positioned during the evacuation process. With the valve closed, it’s just an empty cavity. While evacuating a holding tank, if the body of the valve is mounted horizontally or downward, water, waste particles and tissue residue can easily migrate or literally pour into this void since the seals on each side of the valve do not close together completely with the valve in the open position. Over time, the valve either fails or begins leaking, i.e., allowing seepage when in the closed position and compounding the odor issue. A much better orientation is with the valve body slanted upwards, with the optimum position being straight up so that no moisture can enter that cavity in the valve housing.

In some cases, it may be possible to re-orient the existing valve to a “body up” position by simply loosening a hose clamp and rotating the fitting. In other cases, new fittings may be necessary. If replacing tank valves seems to have become an annual habit, perhaps it is time to consider revamping the termination assemblies into a better configuration.

Valve Maintenance
Typically, the holding tank termination valves are bolted in place between two adapter fittings using a universal, four-bolt pattern. After draining and flushing the tanks, the bolts can be removed and the valve detached from the adapter fittings and removed. Each termination valve can then be cleaned, dried, lubricated and reinstalled. Unless damaged physically, old seals can be rejuvenated by lubricating them with the same Dow 111 grease used on the ASTVDs. To purchase small quantities of Dow 111 lubricant, contact Drainmaster, (www.drainmaster.com).

Speaking of Drainmaster, I’m a big fan of not having to crouch down in the mud, or worse, crawl under the coach to awkwardly pull on a T-handle or yank a cable to open the termination valve. By installing the 12-volt electric Drainmaster gate valve, all the hassles of evacuating the holding tanks can be eliminated. With the sewer hose connected, a simple push of a button will open the Drainmaster valve in less then one second. If you are a serious RVer and you want an electric valve that opens faster and uses less battery current than any other electric valve on the market, you owe it to yourself to check out the Drainmaster valve. To view a short, RV Doctor product review video about the Drainmaster electric valve, please click here.

Sewer Hose
If recreation vehicle waste management is the most disagreeable aspect of the RV lifestyle, then sub-par sewer hoses have got to be the most aggravating component found in the RV waste management system. And frankly, I’m a bit perplexed by this. As mentioned earlier, coach makers must adhere to the precepts put forth in the NFPA 1192, THE standard for how RVs are to be constructed. Likewise, federal, state and local codes mandate how campground sewer systems are to be installed and maintained. Considering the hygienic ramifications of human waste processing, it’s likely to be one of the most stringent of standards in most locales. Yet no standard exists for that crucial link between the RV waste outlet and the sewer inlet in any campground! None! It’s totally dependent upon RV owners to find a suitable aftermarket method of transferring waste from the motorhome system to the campground sewer inlet or dump station. It’s my opinion that coach builders believe their responsibility ends at the motorhome sewer cap and campgrounds believe their responsibility begins at the sewer inlet. Seemingly, both entities bid us good luck in getting holding tank contents safely from point A to point B. And that’s the rub. And why it’s all too ordinary to find spillage, contamination and filth at some RV sites and dump stations.

Most coach builders do supply an inexpensive sewer hose with the motorhome, but it’s not uncommon to find coach owners having to purchase three, four, even five or more sewer hoses per year. And many RVers have a tendency, time and again, to buy those hoses based on price point only. Cheap, thin, wire-bound vinyl hoses will develop pinholes over time. It’s my recommendation to purchase a quality sewer hose once and be done with it. 

Polychute, in partnership with Drainmaster, has developed a type of sewer hose that will probably last longer than the RV. Here's my video assessment of the Polychute hose.

Additionally, Polychute and Drainmaster are leading proponents for developing a written standard for waste hoses. In this day and age, there is no logical reason why the crucial connection between coach and sewer inlet should be further compromised. It’s a sanitation and health issue, really. It wouldn’t surprise me to see, in the future, minimum standards for hose thickness and materials required by NFPA. Personally, I would like to see the sewer hose become a permanently installed component on the RV, (as some forward-thinking coach makers do now), thereby eliminating the need to connect, rinse, disconnect and stow a nasty hose at every evacuation.

Termination Connections
For decades, the method used to attach the sewer hose to the coach termination assembly has been accomplished by first attaching the hose to an adapter fitting with a common hose clamp and then attaching the adapter fitting to the termination assembly by twisting and locking it onto a bayonet fitting. We’ve all seen those four little nubs on the termination connection; that’s the bayonet fitting.

Though in use since the modern era of RVing included holding tanks, there has been an inherent drawback to this methodology. Think about it; twisting a round, pressure fitting with an integral 360-degree rubber-like seal against a hard plastic surface will ultimately distort the seal. In some cases, where the plastic bayonet fitting has become nicked or otherwise damaged, the seal in the adapter fitting can literally be destroyed by the requisite twisting motion needed to attach it. Take a walk through any campground and see how many sewer fittings are actually dripping waste onto the ground right at the site. Likewise, it’s not uncommon to see termination assemblies with the cap in place, still dripping moisture from the holding tanks as the coach travels down the road. The sewer cap is twisted into position onto the bayonet fitting just like the hose adapter. Interestingly, bayonet fittings are not used in any other industry in the transfer of liquids or waste. Literally every other industry uses a type of compression fitting, a threaded connection or a fitting utilizing a cam-type locking mechanism. 
Thankfully, a cam-type locking waste connection is available that eliminates the twisting required by the bayonet attachment. Check out the Waste Master Cam Loc produced by Drainmaster. Any antiquated bayonet fitting can easily be converted to the newer Cam Loc connection. A cam-type mechanism nullifies the twisting action and results in a very secure connection. During my testing, I could not “make” it leak, even on purpose. And no more rusted hose clamps that, once contaminated by virtue of its proximity to human waste, becomes a health risk if an errant RVer slices a finger while trying to secure the hose.

The Other End
Just as important as having a leak-free connection at the termination assembly on the coach, avoiding leaks and spillage at the connection into the sewer inlet is, for the safety and comfort of everyone, also crucial. Since there is no universal sewer inlet size mandated for RV parks or dump stations, you’ll find everything from 3-inch, 3-1/2-inch, to 4-inch and even 5-inch inlets. Always use a progressive, stair-stepped or tapered donut gasket to ensure the connection into the sewer inlet is sealed tightly. Avoid simply sticking the open end of sewer hose down into the inlet and placing a big rock against it! Believe it or not, that happens all too often!

In addition, I firmly recommend a sewer hose equipped with a positive shut-off nozzle at the sewer inlet end. Both the Waste Master hose from Drainmaster and the Polychute hose have the same, multi-seal, positive shut-off mechanism on the nozzle. This not only permits a sure-fire method of stopping the flow, but when the supplied cap on the coach end is affixed, all odors are locked inside the hose itself during stowage. Tell me you haven’t opened a plumbing bay, (yours or someone else’s), and instantly known there was a sewer hose stowed in there somewhere!

Being proactive when it comes to the waste systems on the RV will reap its rewards for you and also protect the environment. If anything, it will ease offensive olfactory torturing to a certain extent. And that will only benefit us all. So how exactly should the holding tanks be evacuated? Great question! Here's what the pro's recommend. Remember, RVing is more than a hobby, it’s a lifestyle!


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If you are in doubt or do not feel comfortable about a procedure, do not continue. Simply call your local RV service facility and make an appointment with them. The advice, recommendations and procedures offered by the RV Doctor are solely those of Gary. They do not necessarily reflect the opinions, procedures and recommendations of our sponsors or advertisers.