23BHE Sewer Smell from Under Bathroom Sink

[geobrian]

First day in new RV. Full hookups at RV park. Grey tank in open position, black tank closed. We have a very strong sewer gas smell coming from under our bathroom sink, like it may be coming from our one-way air vent attached to the end of the black pvc piping under the sink. The sink itself doesn't smell, as there is water in the p-trap blocking the sewer gases. Any ideas what the problem could be?

[FT4NOW]

I'd guess it's what you referred to as the one way air vent. It's called an air admittance valve and can be picked up at any major hardware store. It unthreads from the pipe and is easy to replace. You can remove it and cover the end of the pipe and see if the smell goes away. It has been a fairly common issue for them to go bad from time to time.

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[JCR GD]

^^^^ Yes, AAV stuck open.

FWIW, I always keep all tank valves closed 'til ready to dump. I don't want who knows what coming up into my plumbing. But that's just me.

[powerscol]

First day in new RV. Full hookups at RV park. Grey tank in open position, black tank closed. We have a very strong sewer gas smell coming from under our bathroom sink, like it may be coming from our one-way air vent attached to the end of the black pvc piping under the sink. The sink itself doesn't smell, as there is water in the p-trap blocking the sewer gases. Any ideas what the problem could be?

The admittance valve that FT4NOW mentions may just be stuck. Try tapping removing it and inspecting. It just may have some construction dust preventing it from closing.

BTW I would keep your gray tank valve closed until the tank fills. It may be tied into the black tank vent system and secondly sewer gasses from the park system will back up into the trailer (might be the source of your issue). I also use the gray tank as a flush after dumping the black tank.

Hope this helps

[geotex1]

The standard AAVs are basic quality units, and will stick fairly easily in RV applications. You can replace with higher quality, more dependable models for about $20.

[Houndbb]

First day in new RV. Full hookups at RV park. Grey tank in open position, black tank closed. We have a very strong sewer gas smell coming from under our bathroom sink, like it may be coming from our one-way air vent attached to the end of the black pvc piping under the sink. The sink itself doesn't smell, as there is water in the p-trap blocking the sewer gases. Any ideas what the problem could be?

The AAV simply unscrews from the stack pipe. This happened to us early on and I read all the suggestions for replacing it. Paid particular attention to the “mini” Studor brand, and, yet, it was still too big as our stack had been crammed in the very corner of cabinet front and wall. Then some frugal, intelligent member here suggested that the OEM AAV can be removed and washed. I now do this once at the beginning of each season, and we’ve never had the cabinet stench again.

[Ynot4me2]

Try keeping your gray valve closed for a day or 2 and se if that solves your problem. It's best to keep all valves closed until ready to dump.

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[geobrian]

Thanks all. Keeping the gray tank closed definitely helped. Picked up a new valve today, but can’t get the bad one off. Maybe some dry lube would help to loosen it up?

[Houndbb]

Thanks all. Keeping the gray tank closed definitely helped. Picked up a new valve today, but can’t get the bad one off. Maybe some dry lube would help to loosen it up?

You might try to loosen it with large channel locks (our largest set has jaws with this shape -() set in) or, a VERY small pipe wrench. I’d wrap it with a damp cloth or a silicone sponge. Either tool is available cheaply at Harbor Freight, and I guarantee that you’ll use either one again and again.

[geobrian]

Update. Replaced the air admittance valve recently. Out camping now and still getting the sewer smell from under our sink if I leave the grey valve open while hooked up. I don’t know what else it can be. Only solution for now is to leave my grey valve closed all the time except when dumping.