Toilet burping

Sounds like the vent is plugged. When you flush and the mass goes into the tank, the displaced air has to go someplace. That is what the vent does. If the tank is not vented, that air has to come back out of the toilet, hence the burp.

A mound in the tank causes problems, but not THAT problem. It doesn't block the air from escaping the tank on flushing.

Tank flushing systems only have one sprayer in the tank. It either just sprays like a garden hose nozzle set on "shower," or it rotates spraying as it goes around.

My first step would be to go up on the roof and remove the vent cover. Look for visible obstructions, like a wasp nest. Look to see if the vent pipe may have come loose and fallen down into the tank so it is no longer above the high water line. If it falls down where it is below the high water line, it can't vent once the water level covers the bottom of the pipe. Put a water hose down the pipe and flush it out in case something has the pipe blocked at the bottom where you can't see it.

I once had a MH that developed a sewer odor in the bathroom. I traced it to the under-sink AAV (air admittance valve) being bad. I replaced it and it fixed the problem. Until I dumped the tank and it came back. I eventually figured out that the tank vent was plugged, and when I dumped the tank, it broke the under-sink AAV trying to vent the tank. Once I flushed out whatever had the tank vent blocked, and replaced the under-sink AAV AGAIN, it never recurred.

As far as your question about tank flushing systems. I have one they are not great. I have found that nothing works better than a sudden rush from a 5 gallon bucket of water with valves open, sometimes 2 or 3 buckets before water runs clear. Good luck.

Bobbo wrote:

A mound in the tank causes problems, but not THAT problem. It doesn't block the air from escaping the tank on flushing.

I'll have to disagree with that - I've experienced it personally on 2 different RVs. Our current RV has a black tank that is fairly shallow right under the toilet opening, and then deepens out; like a "step" feature. When we're sitting for a length of time when we flush everything hits the shallow part of the tank and can build up there with no movement to push it to the deeper part of the tank. When we're moving every day the pile gets moved by the movement of the RV on the road. We know when there's a big pile because the toilet burps when we flush. Using a hose to force that pile into the deeper part of the tank works every time.

Thanks. Was think g it might be the vent. I would like one of those scope cameras to look down and inside everything

It could be the vent as others have said but my bet is that the black tank is still full. Go ahead and add more water but keep a close eye on the toilet so that it does not overflow.

I"d go with plugged vent as option A
Option B is the vent pipe dropped down to the bottom of the tank. (Takes a viewing device to figure that out Endoscopes are a few dollars on WISH dot com plug into a cell phone and you need some kind of "Wand" like a quarter inch piece of PVC about 5 feet long)

Sounds like a classic "poop pyramid" prob.

Get one of those flexible wands with the spinner on the end and blast that problem away.

A search on this site should produce a lot of hits