Sewer smell when using exhaust fans

Here's a secret. Put something under your sewer line to create a P trap or do something similar to trap water in your hose. This will prevent sewer gasses from coming back up your hose and through your tanks and vents.

Thanks for all the help. We do open a window when using the exhaust fan, but we didn't refill the p-trap as suggested. Tried that just now and the smell in the sink is gone. The smell underneath the sink is there but much fainter. The air admittance valve has been glued on. Would like to replace, any ideas on how to get it off?

Yep, just open a window and close the grey valve. Your fan is blowing air out and it has to come from somewhere. With your grey valve open you could be sucking gasses all the way from the main sewer system, gag me. Don't light a match, lol.

Open a window when using an exhaust fan.

IAMICHABOD wrote:
I would check and replace the air admittance valves
located near your sinks,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!

X2 on the air admittance valve. JMO

I would check and replace the air admittance valves
located near your sinks,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!

Thanks for all the suggestions and ideas. We live full time in our RV. Most of the folks here leave their gray line open until it's time to drain the black tank. They don't have the problem we are having. Day before we empty black tank, we close the gray tank, use the deodorizer, then flush line with the gray water. Have tried putting water in sinks when running the exhaust fan that's when the smell comes from under the kitchen sink.

Your trap or Air admittance valve should be blocking those fumes. Why are you leaving your gray valve open? Leaving the valve open can be a source for issues including sewer flies.

If you have not run water in the bath and kitchen lately the traps could be dry. Run some water in them if not

Make sure the black and the grey tank both have good vents to the roof of the trailer. The can share the same vent line (1.5"{ ABS is good) and it can be connected to the drain line from the sinks to the tanks. The vent line will allow the sewer gases to escape vertically from the tank, and will relieve any pressure inside the tanks that might force gases past the P-traps. Don't forget that you always have to refill the P-traps after dumping, the suction sucks them dry.

Brian