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. Today he discusses a stinky black tank.
I have a new ATC 5th wheel toy hauler and am having black tank smells in the bathroom. I treated the tank with deodorizers and flushed completely, but as soon as it warms up outside, the smell is back. The water is staying in the toilet and I checked the vents and they seem okay. —Gregg
The first thing I would check is the venting system. Take a look at where the black tank is located. There should be a vent tube that either runs up to the roof or, if it is located directly under the kitchen counter, it will have a “cheater vent” with a siphon cap.
Let’s start with the roof vent
I would start by looking at the cap to make sure it is on firmly. Make sure that the pipe is not loose. I also would take the old vent cap off and install a Cyclone that will turn with the wind and siphon air from the tank out. If you get a good strong wind with the old-style cap, it could force the air back down into the rig.
When you remove the old vent cap, also remove the sealant and check to see if the pipe is loose or will pull up. It is not uncommon for the vent pipe to separate from the black water tank, which means the fumes/smell from the tank can come inside the rig. Typically, it’s difficult to get to the top of the tank and vent tube, so if it’s loose, you will probably need to tear out some cabinetry. Since it is new, I would make sure to document it with the manufacturer or dealer.
If you have a “cheater vent,” there will be a pipe that comes up through the floor in the underneath cabinetry and has a cap over it. This is designed to pull in air to eliminate a vacuum in the pipes when dumping. It is supposed to be designed to only allow airflow in, but they go bad and I’ve had to replace a few. If you have one of these I would not test it—rather, just replace it.
Another issue could be the flange for the toilet on the floor. It could be cracked or not set properly or the toilet could be cracked. It’s easy to remove and inspect. Just take off the plastic base cover and you’ll see the mounting bolts/screws.
These should be the only ways for fumes to get into the rig. I would also suggest using Thetford Tank Blaster along with a deodorizer. And don’t run your roof vent outwards with the toilet lid open!
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