By Mark Polk
RV EDUCATION 101®
RV holding tanks are designed with a vent pipe going from the top of the holding tank to the roof of the RV, to vent the tank and the tank odors. The problem is, holding tank odors accumulate in the tank and can’t really be vented outside because there is no air pressure in the tank to force the gases up and out of the vent pipe.
Another problem occurs whenever wind blows across the vent cap on the RV roof. The higher air pressure forces air down the vent pipe, pushing the tank gases to the only other way out of the system, the RV toilet. Whenever the air pressure is higher inside the holding tank than it is inside the RV, the odor escapes into the RV by way of the toilet, when it is flushed.
There are aftermarket RV sewer vent caps you can install (or have installed) that are designed to pull the odors from the tank up and out of the RV. [Editor: Here’s the 360 Siphon Roof Vent Cap as pictured above.]