Originally Posted by R&TB
Picked up our trailer Thursday and went for a weekend outing. First flush in the half bath and the odor is back. The dealer said he replaced the gate valve seal. They "think" the AAV is in the wall and did not check it. I did consult another dealer and he suggested running the black tank flush with the dump valve closed. Go up on the roof and check for air coming out of the vent pipe. If no air comes out it means the vent pipe is clogged. I am not sure when I will be able to perform this test. I will try to keep you informed.
If the bowl was holding water, the gate valve seal was not the problem. I'm surprised they didn't change the flange/floor seal at the bottom of the toilet. Did they check the toilet for cracks? That sometimes happens.
Another way to check if the roof vent is plugged (better in my opinion), is to run water down it from a garden hose. If the vent pipe doesn't fill up, it's clear. Also, running water down it will wash away any possible obstructions, like mud dauber nests.
Good luck with your problem.