Dear RV Doc, we recently inherited my in-laws' 20-foot 5th wheel. Everything's great except for the holding tank. When we travel it releases a horrible smell. We keep the bathroom ceiling vent closed and the toilet lid closed with some water in the bowl, but the smell continues to escape. Once we have parked and the tank becomes more full, the smell lessens somewhat. I know that my in-laws did a lot of rough camping where they didn't use a dump station. We're wondering how do we get rid of it? Barb, (Victoria, BC)
Venting is the primary method of allowing odors to exit the confines of any holding tank. All holding tanks are vented through the roof of the RV. In most cases, each tank will have a separate vent stack that runs from the top of the tank, up and through the roof. Driving down the road (movement) and peculiar air flow movements over the top of a parked RV (stationary) can and will create a positive atmospheric pressure inside the holding tanks. It’s this positive pressure inside the tanks that force fumes, odors and other airborne contaminants into the living sections of the RV.
Surprisingly, there is no requirement for coach builders to install a vent cap on the roof and those that do, often install an inexpensive cap that can actually exacerbate the problem. Typical vent caps are designed primarily to keep leaves, dust, dirt and critters from entering the holding tank vent pipe. They do little, if anything, to help rid the odors from the waste system. None are designed to specifically aid in creating a negative atmospheric tank pressure. None, except a new type of non-moving vent assembly called the 360 Siphon.
Click the video box to see a short video that shows how the 360 Siphon actually works!