Dear Dave,
I’m not sure of the year of my RV. There are 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
Dear Heather,
I would suggest trying Thetford’s “Tank Blaster” product as it will get rid of most of what I call the “Bad Bugs,” which are anaerobic bacteria that create those rotten egg smells.
Next, I would suggest looking for your vent. The black water tank has a vent pipe that comes up through the coach and is designed to allow air in so there isn’t a vacuum when dumping the tank. Most go up through an interior wall and are seen on the top of the unit.
However, if the pipe comes up in a kitchen area with a countertop, it can’t make it all the way to the top so they cut it off under the counter and use a siphon cap, which we call a cheater vent. These are designed with a gasket that allows air to draw in but does not let the smell seep out. However, they go bad all the time! Find out where your vent is and also make sure it is installed on the tank. I have found them to break off or come loose and the odor comes up through the coach.
RVtravel.com publisher Chuck Woodbury swears by the Siphon 360 vent, which draws air from the black tank out the top of the RV. He tells me that since he replaced his cheap factory installed vent with the Siphon 360 he has no problems with odors.
Good luck!
Dave
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I want to clean my black tank valve but I can’t find it
Dear Dave,
I am living in my motorhome because Hurricane Ian flooded my house. I can’t find the black water tank valve. However, I know where the handle is to open and close the valve, but I want to find the valve itself so I can either clean it or replace it. I have looked all over the place for it. I can’t find it in the service center like the other valves. On another topic, I wonder if I can refill the propane tank without taking it to a dealer. Thanks for your help. —Thomas, 2017 Winnebago Vista 29E
Dave Solberg is a leading expert in the RV industry and the author of the “RV Handbook.”
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I have used a witch’s brew of a gallon of water with a cup of liquid laundry detergent and a small bottle of Calgon…never had a problem with black tank or drain valves.
Will 2nd the opinion on Lippert’s Siphon 360 vent cap. Standard vent caps are good for letting air IN to allow tank draining, but not OUT. Gas pressure can vent through the toilet. The Siphon 360 draws that air out with no moving parts.
Another tip, you should not keep waste tank valves open for a variety of reasons, one being it creates an unblocked connection to the park’s septic system and stinky gas will feed back into your waste tanks.
Thank you, Dave! Safe travels! 🙂
There’s one other place to look for black tank smell. The toilet itself. We started having bad smells after using a non potable water source to flush out the black tank. We had run the hose inside to the toilet as that would be faster than using the outside tank flush. At home we cleaned and flushed using every product available to no avail. Turned out this model toilet allowed water to seep into the base of the toilet so when we used the very stinky non potable water some got into the base. The cure was a new toilet. No more bad smells.
Heather, not quite sure what you meant by “filter.” Be assured there are no filters of any kind in the black tank system.
Next, while this is kind of gross, if you hold open the toilet flush valve and shine a light down into the black tank after you drain/dump it, do you see a bare “clean” tank, or is there residue or a poop pyramid still left?
You didn’t say if you are full time or not. If not, you can try filling the black tank and adding regular septic treatment like Roebic and letting it sit for two weeks, then flushing well.
Finally, are you sure it’s not your grey tank? A failed “cheater valve” under the sink could let grey tank odors in, which can be worse than black.
The AAV, air admittance valve, under the counter top is for gray water venting from that particular sink. Black tanks vent through the roof. It is possible that the vent pipe to the roof has slipped down into the tank and no longer venting.
to check the integrity of the black tank vent piping, drop a few drops (mixed with a quart of water) of peppermint extract down the black tank vent where it passes thru the roof. Make sure there is water in the toilet bowl to form a good seal. If you smell peppermint from within the RV you have an open pipe somewhere, but at least you will have confirmed it is the black tank system and not the gray tank system.
Sometimes its not the black tank making the smell but rather the gray tanks, make sure the the P-traps are full of water and don’t dry out. I installed Cyclone vents on both gray and black tank air vents with great results. JMHO