Sunday, September 25, 2022


RV Doctor: Why does one bathroom sink stink and the other doesn’t?

Dear Gary,
I have two bathroom sinks in my coach: one with the commode and one next to the shower. The one in the hallway of the coach sometimes has a terrible smell and I can’t tell what’s causing it. This has been going on for a few years. I have poured the stuff down there that’s supposed to take away smells, and even used apple cider vinegar. Nothing seems to work. It is just that one drain. Any suggestions? —Kathy P.

Dear Kathy,
Chances are you have a faulty anti-siphon trap vent device (ASTVD) under that sink. It’s a small ABS plastic fitting found near the P-traps under most RV sinks. Its purpose is to allow air into the drain system to help drain the sink at the same time it prohibits gases and odors from coming in from the holding tank and drain piping. It is constructed with a spring-loaded rubber diaphragm. Oftentimes this rubber membrane will dry out and not fully seal against the rising odors out of the waste system. Other times, the spring simply wears out.

If you look under your sink and follow the horizontal ABS piping as it leaves the P-trap, you’ll likely find the ASTVD situated a few inches above this horizontal arm. It’s a simple, screw-on fitting. In some cases, the rubber membrane can be renewed by applying a lubricating grease; I recommend Dow 111 grease. It’s a relatively inexpensive component and is easily replaced by any RV handyperson since it does not require any sealant and is only hand-tightened in place. They can be purchased or ordered through any RV parts department or even online.

Another thing to consider, especially if you need a little more room under those sinks, is to replace all the P-traps with a HepvO waterless sanitary valve. When using a HepvO valve, an ASTVD is not needed at all. Plus there is zero maintenance (no winterizing, cleaning, etc.) when using a HepvO valve. But one of the biggest benefits is the added storage space under the sinks. This is the route I highly recommend! Read all about the HepvO waterless sanitary valve.

And here’s a short video I produced regarding the HepvO valve. You’ll also find more helpful information at the Drain Master website.

Hope this helps! At least it will keep you busy for a while!

gary-736Read more from Gary Bunzer at the See Gary’s videos about RV repair and maintenance.



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2 years ago

Keeping Water in all the traps in your RV is also a KEY!
When RV’s sit for long periods of time, the P-Traps dry out and allows sewer gases to find their way into your RV. Even when you put water in the sinks and other drains you may have a smell. Even your shower drain will produce odors.

As a suggestion, I use a small amount of my liquid RV DIGEST IT chemical in all my drains and sinks when the RV is going to sit for awhile. This helps to keep odors down and helps break up any hair or other nasty stuff that will smell as it decays.

Just a thought!

2 years ago

Personally, I can’t see much advantage. The HepvO has a collapsible membrane that expands and contracts. Like anything else it’s subject to problems….and fixing it requires more than a simple screw on replacement like the ASTVD. If you think you’re really gaining much usable space under the sink maybe you should consider all the stuff under there instead.

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