Friday, June 2, 2023


How can I find an air leak in RV’s black water system?

Dear Dave, 
I bought a toilet chemical thinking it would smell strong enough to trace any air leaks from the black tank. Today’s additives don’t smell. Bought Pine-Sol, same problem. Bleach, same. What can I try next? Odor eliminating additives make the air heavy, with no identifiable odor, just unpleasant. Thank you, Dave. —Francis, 1995 Rialta

Dear Francis,
The Rialta has a very simple waste water system with a telescoping bath design and the toilet sitting directly over the small 13-gallon black water tank. My first question is, what gives you the indication there is an air leak?

The vent pipe comes off the tank and goes up to the top through the wall behind the driver seat, and the drain pipe comes off the bottom of the tank. If there was any type of leak in the tank or drain pipe, you would see liquid from that underneath. Here is the parts diagram from the Owner’s Resource site on the Winnebago website.

The shower is called a wet shower, which means everything gets wet when you use it and the bottom of the room is the shower pan. The toilet drains directly into the tank and the shower pan has a small drain, which is #18. The water is actually pumped by #13 to the line going to the top of the tank. The pump has a check valve, so no water or odor can come back out.

You can download a copy of this diagram here.

Also check the spade valve and vent

If you are getting a sewage smell inside the rig, I would suggest checking the spade valve of the toilet by putting in some water to see if it stays in. If it drains, the rubber seal is not seating and will allow odors to come in. Make sure it is seated around the edge and not pinched. You can try to condition it; some even use Vaseline.

Next, I would check the vent on the top of the rig. If the pipe coming out has cracks or gaps around the sealant, wind can whip in while driving or on windy days and could force some odors inside, as well. If the cap is off, it can also get wind inside. I would suggest replacing it with a Cyclone-style cap.

 You might also enjoy this from Dave 

Black tank still smells after trying EVERYTHING

Dear Dave, 
Not sure of the year of the RV. I am having very strong odors after flushing and I have cleaned the black tank with EVERYTHING. I have had it flushed and all seems well, but in a day or two it is back to being foul. I’m thinking it is the filter or siphon but I do not know where to locate these and pinpoint which it is. Why does my black tank always smell? —Heather, Wilderness Advantage Extreme Edition

Read Dave’s answer.

Dave Solberg is a leading expert in the RV industry and the author of the “RV Handbook.”

Read more from Dave here


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Dave Solberg
Dave Solberg
Dave Solberg is a leading expert in the RV industry and author of the “RV Handbook” as well as the Managing Editor of the RV Repair Club. He has been in the RV Industry since 1983 and conducts over 15 seminars at RV shows throughout the country.


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Tom Relyea
21 days ago

If the concern is sewer smell getting in the rv, a smoke test can be performed. It is easier to find a leak in vent or a bad seal with smoke rather than smell. There are testing companies that can do the test.
Retired plumber

21 days ago

Not sure if this applies in a wet bath but my issue was the seal from the toilet to the floor was allowing black tank smelliness into the trailer.

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