Do you have a washer/drier in your coach? Is it located in or near the rear bathroom. If so, are you using it on a regular basis? If you yes to the first two questions and no to the last, it could be your problem. We have to add water to the W/D drain to keep the trap filled if we aren't using it on a regular basis. It is very difficult to identify exactly where an odor comes from in my experience. If the trap for the W/D dries out, it will allow gases from the grey tank into the coach.
The air admittance valve or vacuum breaker should be a one way valve that allows air only when there is negative pressure of the drain. It's purpose is to keep water draining from the sink from siphoning the P (or S) trap leaving no water in the trap to prevent gases entering through the drain trap. It should never allow air to flow in the opposite direction if it is functioning properly. If there is water in the trap for the sink and shower then they wouldn't allow gases from the grey water to enter the coach.
Thanx so much for this info. We had this problem a few times during our trip from Maine to California and back (2015) and it almost drove the 2 of us nuts. I have nose for smells, husband is retire pipefitter so we tried a lot of things, and I had narrowed it down to w/d....but didn't know the why. We had a great trip but every day brought a new challenge .... from cupboard door latches, to lights, batteries, and fridge problems. A real experience across a beautiful country. We are from New Brunswick, Canada so it was a treat to see some new things. The things advertised as "must sees" were not the rule though. The off the beaten track were where we had the best adventures.
Sewer Gas Odor Inside
in Water and Holding Tanks
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Thanx so much for this info. We had this problem a few times during our trip from Maine to California and back (2015) and it almost drove the 2 of us nuts. I have nose for smells, husband is retire pipefitter so we tried a lot of things, and I had narrowed it down to w/d....but didn't know the why. We had a great trip but every day brought a new challenge .... from cupboard door latches, to lights, batteries, and fridge problems. A real experience across a beautiful country. We are from New Brunswick, Canada so it was a treat to see some new things. The things advertised as "must sees" were not the rule though. The off the beaten track were where we had the best adventures.