Last week I replaced the closet flange seal on my Thetford toilet because I was getting odor in the bathroom when driving or when my fantastic fan was on. At the time it seemed to have worked, but I guess I spoke too soon.I have plugs in both the bathroom sink and shower drains. The air admittance valve under the sink is brand new and seems to be functioning...no odor under the sink. There is a good 1/2 gallon of water in the toilet bowl. I'm stumped. I don't know what else to do.

Did you make sure your black tank vent on the roof is not clogged?

Look under the bath sink for a vacuum check above the P trap. If it is weak, fumes can be sucked into rig.Air admittance vent

Recently, each time we drove the MH, after about 10 miles we'd get a strong sewer smell also. Figured out it had to be one of the sink drain line vents that weren't venting properly. After doing some reading, the mfgs recommend changing them out every ten year - our were about eleven years old. Changed all three since I wasn't sure which one was the problem. No more odders.I first went to Home Depot and bought three of them. Went back to the MH and got two of them installed. On the third one, it was right up against the sink and the ones from HD were too large of a diameter to install. It took a while, but I finally found some at an RV place that had the same small diameter as the original ones.Look in the picture just to the right of the sink at the top of the black plastic pipe - that's your vent valve. Just unscrew.Bill

I had this too and it turned out to be the slide seal was leaking ,yet it would hold water. don,t no how ,but changed the slide seal and it was fixed.

To those suggesting it's the air admittance valve, I stated in my original post that it is brand new and functioning correctly. There is NO oder under coming from under the sink. I have not yet checked the vent on the roof. Just looking at the physics of this, it seems that if it was clogged, air couldn't get in. If air can't get in through the vent on the roof, how could my fantastic fan pull air into the RV from the black/grey tanks? You can't pull air through a straw if your finger is on the other end. :/

It's back....and I'm stumped | Good Sam Community

43 Replies

Trackrig
Explorer II
Feb 12, 2016
Recently, each time we drove the MH, after about 10 miles we'd get a strong sewer smell also. Figured out it had to be one of the sink drain line vents that weren't venting properly. After doing some reading, the mfgs recommend changing them out every ten year - our were about eleven years old. Changed all three since I wasn't sure which one was the problem. No more odders.

I first went to Home Depot and bought three of them. Went back to the MH and got two of them installed. On the third one, it was right up against the sink and the ones from HD were too large of a diameter to install. It took a while, but I finally found some at an RV place that had the same small diameter as the original ones.

Look in the picture just to the right of the sink at the top of the black plastic pipe - that's your vent valve. Just unscrew.

Bill
enblethen
Nomad
Feb 12, 2016
Look under the bath sink for a vacuum check above the P trap. If it is weak, fumes can be sucked into rig.
Air admittance vent
gbopp
Explorer
Feb 12, 2016
Did you make sure your black tank vent on the roof is not clogged?

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It's back....and I'm stumped

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