Cracked Water Tank on Pop-Up Camper

How do I fix a white polyethylene fresh water tank in my older Starcraft pop-up camper? I've removed the tank and cleaned it. I stopped drilled the crack. I've roughed up the vicinity of the crack with emery cloth and a course sanding disk. I've cleaned the area with alcohol. I'm ready to apply the patch. But before I do, I wanted to get with you concerning this and get your opinion. I'm leaning towards a fiberglass patch and epoxy. The Eternabond also looks and sounds good. I'm also researching using the thermal catalytic plastic fusion method. Please let me know the route to take. Thanks! Greg E., (Monument, CO) 

Greg, I believe your best bet is to have the crack repaired by plastic welding. It’s the only type of repair I would guarantee not to leak at any point in the future. Patch kits (available in the aftermarket) are great for a temporary repair, but with the racking and twisting going on inside an RV, it will likely crack again. 

It’s also important to find out why it cracked in the first place. If undue stress is placed on the tank, (by its design or installation technique), it will likely leak again unless a skilled plastic welder performs the repair. I used to teach this repair method to RV service technicians with great success. Any thermoplastic can be welded whether it be a fuel tank, waste holding tank or a fresh water storage container. Here’s an index of similar questions I’ve published in the past.

http://goo.gl/2sVZs

Now, that said, and given your tank is relatively small since it’s in a pop-up, you stand a better chance using a repair kit than say, a large container from a 45-foot motorhome. I’d try the Eternabond method first; especially if there is no stress at the crack location. Fiberglass patches will not adhere properly to polyethylene. So I’d suggest either Eternabond tape or one of the commercial two-part epoxy kits if you cannot locate a shop with a plastic welding machine. The last resort is to replace the tank with one with thicker walls.

Leaking Holding Tank

I have Dodge motorhome with a leaking gray water holding tank. I have found several cracks where the hangers hold the tank to the underside of the RV. What is the best method to repair the tank? Charles, (Berryville, AR)

Charles, I'm guessing your tank is mounted with brackets similar to those in the photo at left. I receive a lot of inquiries regarding cracks in plastic tanks; black and gray holding tanks, fresh water holding tank, plastic gasoline tanks, etc. Click here to see my most common response to your question.

(Note: The response to Charles above was edited in the spirit of consolidation for inclusion into the Q&A Archive)

Thermoplastic Welding

I don’t have much experience with an RV, but I do have a polypropylene gas tank on my Dodge Ram 4x4 and it has a leak in the bottom. Do you have any suggestions on repairing this without removal of tank? I have tried some of the fiberglass repair kits but they did not hold.
Frank, (Savannah, GA)

Frank, the good news is that polypropylene, being a thermoplastic, can be successfully welded. Other thermoplastic tanks common to RVs are made from polyethylene and ABS; all of which can be safely welded. Cement-type repair kits, as you’ve found out, simply will not repair a plastic tank permanently; welding is the only viable method of a permanent repair in my opinion. Another plus, plastic welding can be performed safely on polypropylene gasoline tanks since the practice employs hot air or nitrogen rather than arcing and sparking. Simply draining the tank is all that is necessary. Remember though, the area must be clean and dry to effectively weld. The downside is that it takes specialty equipment in order to weld plastics. Check with your local RV repair facilities. Many shops have plastic welding machines since the same technology is used for polyethylene water tanks and ABS holding tanks as mentioned above. Some RV repair shops will indeed have a welder. Finding them is the difficult task. Let your fingers do the walking first.

By the way, if you'd like to learn how to do this yourself, drop me another email. I have a videotape that teaches pro technicians how to weld plastics.

(Note: For a similar question, that bounces back to the response above, check out this post from another reader)

Plastic Fuel Tank Repair

I have an old Vogue II motorhome. It has a large black plastic fuel tank with a 2-inch long split in it. Can it be repaired or where on earth can I find a replacement?
Mike, (Desperate, CA)

 

Mike, I get a few letters each year regarding your exact problem. Check out this post for my usual response to a damaged plastic fuel container question.

(Note: The original response to Mike was edited here in the spirit of consolidation of the RV Doctor archive) 

Holding Tank Damage

While driving, my gray water holding tank dropped down and ground a hole in one corner from dragging on the ground before I could stop. Are there patch kits for ABS tanks? How do I go about repairing the tank without replacing it? Thanks!
John, (Garden Grove, CA)

John, though many patch kit makers extol the benefits of their products quite convincingly, experience has taught me that the only way to permanently repair a plastic tank with bottom damage is by welding. However, I do recommend the patch kits for small holes located on the top of an ABS tank.

Though a bottom corner hole would indeed be tricky, a good plastic welder should have that repaired in a relatively short time unless the plastic is very thin in that location. Some, but not many, RV repair facilities offer professional plastic welding services. You'll have to call around to find one in your area. If you happen to find a service center that has the professional equipment, but no knowledge of how to use it, (it happens), I do offer an instructional videotape that details the steps necessary for successful plastic welding. Feel free to email me if you are interested in the training video. Relatively inexpensive plastic welding devices are readily obtainable if you wish to attempt this yourself if no shop near you is properly equipped.

Drippin' Tank

I have an older Georgie Boy Cruise Master. My wife and I bought it last year and enjoy it very much. However, I have noticed that the black water tank leaks when it is full. At first I thought it might be cracked but then I read an article that said the vent pipe may have dropped down. Can you give me an idea of what to look for? If I have to pull the tank will it be a major undertaking?

Jay, (Menominee, MI)

Jay, it's quite possible you have a crack at or near the top of that particular tank. A very close inspection is recommended. Sometimes it is possible to crawl under the rig and use a mirror and a flashlight to see the top of the tank, though that is entirely dependent on the exact installation on that model coach. In some instances, frame members may impede your view, or the tank may be positioned flat against the under-flooring.

First drain and flush the tank numerous times (it had to be the black tank, right?), and then begin filling the tank with fresh water. A garden hose into the toilet will probably be the quickest method though speed is not the point. As the tank nears capacity, closely look with that mirror and flashlight to see exactly where the leak appears first. It's common to see cracks on the sides of the tank near the top; rarer are cracks on the very top of the tank. It could simply be leaking from around the 3-inch pipe from the toilet or the smaller vent pipe requiring nothing more than new sealant.

If a vent pipe were to drop it usually drops into the tank through a rubber tank fitting. This may or may not cause an actual tank leak. You can check the vent pipe from up on the roof. Remove the sewer cap for that vent line and look for the ABS pipe. It should stick up about an inch above the roof. If it is much lower than the roof line or not visible at all, then it may have indeed dropped into the tank.

But I digress….If it's not possible to view the top portion of the holding tank from below the motorhome, then yes, the tank will have to be dropped. It may be suspended by hangars or angle brackets. It's not a difficult task though it is time consuming to remove the holding tank.

First remove the toilet and the floor flange as well as the vent pipe that extends up through the roof. It may be necessary to cut the ABS vent pipe close to the floor line and use a coupler fitting after reinstallation. It is also necessary to remove the 3-inch tank outlet fitting and to disassemble the termination assembly, thereby isolating just that tank. It seems like a lot of work, however, it is simply a matter of logically taking apart a puzzle. After the tank has been removed, reinstall the closed termination valve to block the outlet, support the tank and refill it while on the ground. It will soon be evident where the leak exists. Or the crack may be quite visible after dropping the tank.

Plastic holding tanks can be successfully welded using a plastic welding machine, but not all repair shops are equipped with a plastic welder so you may have to shop around. Avoid using an aftermarket patch kit. The only viable method of repairing cracks in plastic tanks is by welding. Patch kits can, however, be used in an emergency situation or for a temporary repair. Keep in mind some repairs may just not be feasible; existence of numerous cracks, deteriorated plastic, impact damage, etc. In those extreme cases a new tank is in order. Always install the largest possible tank that will safely fit in that same area.