Our toilet has started to burp when flushing. No poo pyramid, we keep the black tank valve closed until time to dump. The tank also gets flushed well after dumping. I'm thinking the vent much be clogged. First thing I'll check is the vent cap on top. If nothing can be seen from there, I will have to try clearing out the stack. Considering the vent stack has two 45° elbows in it, I was thinking about compressed air to try to blow through it. No more than 10 psi, with the black tank valve open. My question is does anyone know how well the factory glued the stack piping and fittings? I wouldn't want to blow the piping apart.

I wouldn't risk using compressed air. My buddy Terry had his vent line become detached and it put grey water into the basement and the coroplast area, a poor joint. No fun cleaning up!

We've had burping before, cured it via filling the tank and back flushing a few times. If you fill the toilet with water then flush it may clear, but you may get some water on the floor as well!

That's what I was afraid of, the stack coming apart, or breaking the seal at the tank. I think I will run a fiberglass fish tape down the riser if the vent cap isn't the issue. I kept some short sections of fish tapes when they got broke on the job, so it won't be a big deal to contaminate one.

I have done the fish tape and running water down the vent thing to no joy. Always comes back to a poop pyramid. We have an MB so the front toilet needs to have a lot of water when flushed. The tank entrance design is bad. And the tank needs to be full when dumping. And full when flushing. I have timed how long it takes to fill the tank with the flush system. I use that time as a guideline depending on water pressure.

Rick

I had the same thing happen when I first got my RW. I took my old water hose and cut the end off. Hooked the other end to the hot water fitting for the washer machine and fished the hose down the hopper and let the hot water run it fixed the problem no blow back in the past 2 years. I also put water down the vent.

I have done all of the above with little to no success. I finally went to Camping World and purchased a Flexible Tank Wand. I was amazed at the amount of 'stuff' that washed out of the tanks! This thing jets water into the tanks to clean out extra debris and wash the tank walls.I use with tanks open of course and do this procedure every time I empty. It's a bit of a pain as you need to attach to a hose, take inside the coach and insert in through the toilet, but completely took care of the issue. Also note . . . you'll want to shut off the water to the coach during this procedure.

Well, worked on it over the weekend. I don't think things have been right with the black tank since we bought it a few months ago. Water backed up to almost the toilet. The level indicator said 2/3rds, so I tried to dump. Nothing came out. Tried running a snake down the toilet, I didn't think that would do anything, and it really didn't. I'm set up with hard pipe septic system, so I ran the snake through the discharge valve, nothing.... Got out the shop vac with the 1 1/2" hose attachment and run that down the toilet. Got about 5-6 gallons out before it seemed as if the tank was empty. I did get something interesting out though. A wad of baby wipes that barely fit up the 3" pipe to the toilet. About the size of a baseball. We don't put wipes in the toilet, so they must have been in there when we bought it. Ran water through the toilet, seemed to be okay. Level said 1/3rd. Tried running a bunch of water through the toilet, got to 2/3rds, when to dump, nothing... Came back in level at empty. Dump valve is obviously not sealing when closed. Ran the tank flush and verified that was true. So, it was a combination of two problems. We have been rv'ing for 5 years and know how to take care of our black tank, so a poo pyramid was the farthest thing from my mind.

Well, worked on it over the weekend. I don't think things have been right with the black tank since we bought it a few months ago. Water backed up to almost the toilet. The level indicator said 2/3rds, so I tried to dump. Nothing came out. Tried running a snake down the toilet, I didn't think that would do anything, and it really didn't. I'm set up with hard pipe septic system, so I ran the snake through the discharge valve, nothing.... Got out the shop vac with the 1 1/2" hose attachment and run that down the toilet. Got about 5-6 gallons out before it seemed as if the tank was empty. I did get something interesting out though. A wad of baby wipes that barely fit up the 3" pipe to the toilet. About the size of a baseball. We don't put wipes in the toilet, so they must have been in there when we bought it. Ran water through the toilet, seemed to be okay. Level said 1/3rd. Tried running a bunch of water through the toilet, got to 2/3rds, when to dump, nothing... Came back in level at empty. Dump valve is obviously not sealing when closed. Ran the tank flush and verified that was true. So, it was a combination of two problems. We have been rv'ing for 5 years and know how to take care of our black tank, so a poo pyramid was the farthest thing from my mind.

One bit of advice!!
DO NOT, NEVER EVER use a snake in the toilet or any drain on a rv!!!
First it doesn't work on a big square tank, #2 everything is plastic or rubber, #3 you'll most likely do more damage than good. Some of the drains have Hepvo traps, as opposed to a standard P trap, that have a rubber membrane in them that a snake will totally destroy, then you'll be wondering why you have a sewer smell throughout your rv.
As for the sensors, I wouldn't count on them to tell you anything other than the pretty red lights have power. They are notorious for being so inaccurate to point of being useless. Never looked at ours.
I dumped/rinsed our black tank once a week & if the black got full sooner would let me know by the toilet burp.
When traveling I would add 5-10 gallons of water to the toilet with a good healthy squirt of dish or laundry soap which sloshed around keeping everything liquefied. NEVER had an issue in 10 years of fulltiming.
Your valve leaking probably has some of those wipes hung up in the valve. If you get the tank cleaned good you might dry running a hose from the sewer hose connection outside back into the tank & might get lucky enough to backwash whatever is in there out, otherwise you'll have to take the valve apart, either could be a s####y mess.

Actually, using a hand snake in the toilet won't hurt a thing as long as the person using it isn't trying to punch a hole out of the bottom of the tank. It will help break up a pyramid. I agree not using a snake on Hepvo traps, but there's not a trap on the toilet. I also somewhat agree with the sensors being somewhat inaccurate, but I have also found that when tanks are properly maintained, they pretty much work as designed. We haven't had a problem with any of ours either until I ran across issues that were caused by the previous owners.

I would use the wand with water pressure for any toilet pyramid & NEVER a snake, but it's your rv.

As an update. I finally got around to changing the black valve. When the original was fully closed, there was still an inch or so of travel needed to block the hole. The valve stem didn't have a set screw in a collar to attach the cable, it just had a hole in the shaft that the cable was run through and bent over. New one closes correctly. The replacement wasn't too bad of a job to complete. Everything seems to be good now.