If you have ever had a foul smell in your RV and couldn’t figure out where it was coming from, we may have the answer for you. The HepVo Waterless P-Trap!
All RVs with holding tanks have a vent pipe secured in the top of the holding tank and going up through the roof, which is where the odor created in the tank is vented. In addition there are the tank inputs coming from the sinks and toilet as well as the shower. To prevent odors from coming into the coach from these devices, other products had to be installed inline, the most common used in the sink and shower drains is the P-trap.
P-trap. 
A P-trap uses water in the bottom of it to isolate the coach air from the tank air. You may also have an anti-siphon trap vent device (ASTVD) under the sinks. It is a small ABS plastic device fitting found near the P-traps under the sink. Its purpose is to allow air into the P-traps under that sink, and at the same time prevents sewer gases and odors from coming in from the holding tank and main piping.
ASTVD Vent
A typical roof vent prevents water from entering the tank from the vent and in addition creates a venturi action as air passes through the vent cap.
There are a variety of different designs for P-traps, ASTVD devices and roof vents, yours may look different from the photos but they all work in principle, the same.
The issue we explore in this blog is the P-trap itself as it relates to RVs.
As shown in the photo above the water in the trap is the isolater between the inside of the holding tank and the inside of the RV. Gases do not leak through water and as a result, it is a simple method currently used almost everywhere. The issue with water P-traps in RVs in particular is the fact that the RV moves and can displace the water breaking the isolation barrier, allowing the gases to come into the living space of the RV. Another issue is the amount of space a typical P-trap takes up, especially under the shower drain. A lot of RV manufacturers are now using a new device called HepvO, to solve the space issue.
The HepvO is a waterless p-trap!
The HepvO allows water to flow through it, but does not allow it OR sewer gases to go the other way. Simply put, it is a “check valve” of sorts. The product is not a lot bigger than the drain pipe itself , approximatly 7 1/2″ long by 2 7/16″ in diameter maximum. In most cases the standard P-trap can be replaced with the HepvO which comes in two sizes 1 1/4″ and 1 1/2″. The size you would need is determined by the sink down pipe size. The kits come with the most common fittings needed. Addditional fittings, adaptors etc. if needed, can be obtained at a local hardware or plumbing store.
The HepvO valve has been used in most other countries world wide in housing as well as commercial buildings and will be in North America in the future, after plumbing code approval. The product is listed currently and a building inspector can approve its use. The RV Industry’s RVIA has approved its use in RVs.
For more information about the waterless p-trap, go to www.hepvo.com or call us 877 787-8833 toll free.