Odor from bathroom fan vent

[donellen30]

During our trip last week, we noticed that every time we ran the bathroom fan vent, a strong odor of sewage came into the bathroom. The odor was only noticed during the fan operation and was really bad. We normally only run the vent when we use the shower. Any suggestions on what could cause this?

[cinbob]

Probably odor is coming from black water tank thru toilet when fan is on. Suggest flushing black water tank and adding a deoderizer to it.

Bob

[Terry]

Which direction were you running it? If you were pushing the air out, then you really should not have much of a smell unless you flush the toilet. It should be sealed all around so no gas should be escaping. If you were trying to blow air in, then you might be getting it from the vent pipe on the roof.

Also - did you have enough windows open in the coach? The air is going to come in from the point of least resistance, but if there were no windows open it will try to pull from somewhere.

[hammerdown]

Probably coming from the black tank, always keep about a 1/2 inch of water in the toilet, this will help seal it. Never flush the toilet with the fan on.

[donellen30]

Thanks for the suggestions. I don't think our fan can be run anyway but out. The toilet was not being flushed and had plenty of water in it. We back flushed the black tank this weekend and will see what happens in the future. I will see if the fan has a reverse on it.

[Crabman]

That fan is somehow drawing sewer gas from the black tank. Mine will do it when flushing, but only momentarily. If the toilet holds water then that seal is not compromised. That would seem to leave the toilet flange seal under the toilet or the vent and its piping to the black tank as the possible culprits.

[82corvette]

Always have a vent or a window open when running your fan. The smell might be gray tank odor being pulled from the under sink vents.

[donellen30]

AC was running at the time, so no windows were open. Grey tank had been left open as we were camping for several days, but black tank was closed and about 1/2 full. We back flushed the black tank when we packed up after this trip, so hopefully that will help. My concern is the black tank vent and if the odor could be coming in from there. We usually only run the fan when we are using the shower, and that is when the odor is occuring.