bathroom smells while travelling

the sink in the bathroom does not drain into the black tank, it goes into thr gray tank.

Forget the bandaids. You have a problem. Either something is broken, a vent, etc, or the previous owner was clueless as to black tank maintenance and might have even created a nice little "poop pyramid" for you. Clean your black tank out (takes some time and is not easy) and start over.

My favorite reply is the "pee trap."

Could also be the seal under the toilet where it bolts to the pipe flange. Had the same issue and that was the fix. The old gasket was about as flat a piece of paper. New gasket was about 1/2 inch thick.

I agree the air admittance valve under the sink is a very likely candidate. But one odd one I ran into a few years back while troubleshooting a long standing similar odor issue for another camper was that they did not use the onboard shower, opting instead for park showers. The smell was coming from the shower drain simply because any water that had been in it had long ago evaporated. The amount of stuff that was stored in the shower stall made it difficult to narrow down the source. A couple of layers of vinyl tape over the drain fixed the problem.

D.E.Bishop wrote:

What is logical is that the Air Admittance Valve is Bad. I had that trouble with my Adventurer and replacing the literally $0.98 OEM AAVs cured the problem. I bought a couple from Lowes or Home Depot at about $9.00. Recommended by several folks here.

+1 Like others have stated, replace the air admittance valve. We've had the same issue and that fixed it.

old guy wrote:
I am not one for dumping bleach into a black tank, for one thing urine and bleach gives of some bad fumes . . .

Bad fumes? Oh, is this the bleach-and-urine-make-poison-gas argument?

old guy wrote:
. . . and two it also destroys the bacteria in the black tank

So what? An RV tank is a holding tank, not a septic field. Any bleach in your black tank will most likely degrade before it hits the local septic field.

If you have covers over your crank-open roof vents, they can really help get a suction going as you drive down the road if the roof vents are open compounding any seal/vent/trap issues. Roof vents closed when travelling!

36guy wrote:
Just bought a 29 foot Itasca class c, an 03 e 450 chassis, the bathroom smells like sewer while travelling. The toilet holds water, the seal appears to be ok, any ideas?

I'm not sure how fumes from the black tank comes through the toilet if the bowl holds water, not logical.

What is logical is that the Air Admittance Valve is Bad. I had that trouble with my Adventurer and replacing the literally $0.98 OEM AAVs cured the problem. I bought a couple from Lowes or Home Depot at about $9.00. Recommended by several folks here.

I am not one for dumping bleach into a black tank, for one thing urine and bleach gives of some bad fumes and two it also destroys the bacteria in the black tank