Lav odor

Question

We have an intermittent odor coming from the bathroom when driving. It seems to be related to the drivers or passenger window being open. The toilet bowl seals properly as evidence by water remaining in the bowl and the smell is different than from when I dump the black tank so I suspect it to be from the grey tank.
Attached to the sink drain downline from the P trap theres what appears to be a one way valve. It would be to relieve negative pressure in the tank as it allows airflow into the drain stack. It was a bit loose so I tightened it but the smell still occurs, although not as often or strong now.

My RV has two vents at roof level from plumbing which I assume are from the grey and black tanks. If thats correct and the grey tank is vented to the outside why is this one way valve installed to begin with?
Also if this assumption is correct, I'm considering eliminating the valve and capping the drain stack under the sink.

Can anyone shed light on this for me?

iamichabod · Answer

I would replace the air admittance valves
located near your sinks,do not cap them off,they are cheap and can be found at most big box stores like Home Depot and Lowes as well as smaller hardware stores.

If they fail they will let the smell from the grey tanks in and believe me they can smell just as bad as the black tank if not worse.

Changed mine out and the smell was gone!

old-biscuit · Answer

The Air Admittance Valves are installed downstream of 'P' traps to allow additional air into drain line when dumping grey waste tank. This prevents a vacuum (low pressure zone) in line which would suck the water out of 'P' trap during dumping.

They can weaken and not fully close which allows grey tank odors inside RV

Smells can also come back in by sucking vapors from roof vents in thru open windows

Put a baggie over AAV under sink and secure with rubber bands.......test drive.'
Smell gone with windows open/driving.......then replace AAV

Still getting smells.....might need different roof vent caps (venturi style)
OR shower 'P' trap dry???

gmandjm · Answer

AAVs do go bad.

Also, it's possible that the water is sloshing out of your P-traps as you drive, allowing grey tank odors into your camper.

Try putting in the sink strainers/plugs and closing the bathroom sink and shower drains when you drive.

60sgood · Answer

Air Admittance Valve. Can you tell I'm new to this RV'n thing? Ill bag it and take it for a test drive Old-Biscuit. Ive driven with draips plugged GMandJM but still had the odor.
Shower's ruled out as its not in the bathroom but smell definitely in there.
Thanks guys.

ghsebldr · Answer

60s  I've had the same problem with my class c , but only with the front windows down. Replaced the aavs and had the same problem. Fixed it by rolling my front window up. I have never experienced the problem with the front windows up even with some of the back windows and all 4 vents open. Avoid the smut, roll em up.

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Lav odor

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