Black tank leak

[AbdRahim]

Any Forester owners fix a small leak in black tank, which only occurs when full? I cannot figure out how to get to the connections at the top of the tank, as the tank goes through the top of the storage bin. I have the 2801QS, 2015.

Is it ever possible to have a camping season without issues?

[Duckogram]

I had a leak when full issue on my Class A. It was caused by the dealer when they removed the black tank to get to the sensors on the gray tank. It was the collar seal below the toilet bowl. I was able to remove a panel and seal it up with flexseal. I’m wondering if you can get to it if you remove the toilet and mounting flange? They are usually straight drops. (or is that plops) My sensors never worked well so I tried not to let it get full after that.

[AbdRahim]

Not sure what to do from the inside. I am trying to determine the source of the leak. The connection seems to be between the bathroom floor and the ceiling of the storage compartment housing the bottom of the tank.

Btw, Dawn dishwashing liquid (blue) work wonders on sensors. Large regular amounts.

[Duckogram]

My vote is still for the collar seal.
I do use Dawn to clean the tanks and sensors but my issue was with the wires either not being connected or coming loose even with red stuff on the threads. Not a problem on the 2800.

[AbdRahim]

Do you know how to get to the seal to check?

[Duckogram]

I have no idea. I would assume that the compartment the dump valves are in has no top so if you remove the toilet bowl you should be able to access it. Problem is that you may not be able to see the seal without removing the mounting flange and dump tube. If you have to do that, I dont see how you are going to find a leak. The only other way I can think of would be to try a flex inspection camera if there is room to get it on top of the tank from the dump valve compartment.

Then there is the vent seal which is also on top. You should be able to see your sensors on the right side and dump on the bottom so unless you have a crack, thats all there is.
If you do have a crack it will need to be plastic welded.

[AbdRahim]

Talked with mobile tech today. He says solution is tank replacement. No way to get to the top of the tank without cutting pipes. Told me dealer might do it but he could not. Spoke with another camper today who said his fifth wheel does the same thing. He says there is often no sealant at the joints of the vent and toilet collar and the black tank. I guess I will have to live with it. Hopefully, no more extended stays in the shop. Let's go camping.

[Duckogram]

Understood. If you ever want to try something you should be able to remove the flange and pull the tube out of the seal from the top. Then after cleaning the pipe and the seal, you should be able to use some RTV or flexseal on the pipe and slide it back in. If its the vent pipe leaking, your out of luck and its 3/4 of a tank for you.

Edit: I have not looked but I am assuming the 3” pipe is straight from the flange into the tank.

[AbdRahim]

I guess I will go with 2/3 - pulling the toilet is beyond my skill level. If at a full hook up site, I dump the gray every day anyhow. Don't boondocks (truckstops & rest areas, I use theirs.