Bathroom gas odor

[Ntmoser]

We own a 2014 tracer RBS 2750. We bought it brand new in June 2014. We had no problems for a year. Took it in for our yearly maintenance in May of 2015. Went on our first trip the following June. After about 3 or 4 days of showering we started getting a gassy odor in the bathroom. The first thing we checked was the toilet. But narrowed the odor down to coming out from under the sink, after showering. We took it in for repairs and I also emailed the manufacturer, who suggested a faulty p trap. The dealer had it a couple times and finally changed out the p trap. We thought it was fixed, we took it down to a local campsite for a month and a few showers into camping, we have the smell again. This is our first RV, and I can't live with the smell, any ideas? It will be going back to the dealer as soon as we can get it in. Thank you!

[Ford Idaho]

Are you leaving the gray and black tank drain valves open?

Fan on when showering?

Water in the toilet bowl a couple inches deep?

[Flybob]

Use a flash light and check the plumbing under the sink for a RV tank vent check valve ( see photo). These are notorious for sticking open and allowing odors to enter the living area. If one is found, try tapping it ( Temporary fix) then have dealer replace it.

[Iwannacamp]

I had a similar instance..after traveling. I think in the end it was the grey tank and loss of trap fluid. I put some grey tank conditioner in the system and it got better. I think a gallon of bleach and a few miles would help too.

[Ntmoser]

We've had the valve replaced. So this valve is not the p trap? These rv maintenance people really have to be followed up on.
We're not leaving any vents open, fan is on when showering and water is in the toilet. We have also put chemical in both grey and black tanks.