We had that problem a few years ago in the MH. It may be a design or manufacturing flaw. Vent or flush pipes inserted too far into the tank? I actually had the problem with my home septic tank a couple of years ago. Sewer pipe was only a few inches from the wall on the other side of the tank from entry point. Had to cut it back several inches.
The problem come from the dreaded "Black Pyramid
" building up to high.
Yep, just what you think it as. If you see a bubble, its time to clean it out!
Our solution was a home made tank cleaner. Off the shelf units just wouldn't clean it out and forget about snakes and plungers!
I made one using a 1/2 in. PVC threaded end cap with 1/8 inch holes drilled at different angles. Attached that to a six foot length of water hose using a barbed/threaded plastic coupling. Have to drag a hose in from shore water, on board pump has insufficient pressure. Seems that TP greatly adds to the problem, so only dirty TP goes into the tank. Also, dumping the tank too often and then not putting enough water in after the dumping can contribute. Sitting in one spot for extended period could also add to it. Things just don't get moved around enough!
Haven't had to clean my out for a while now.
'01 National RV Tropi-Cal, Ford V10, '01 Suzuki GV 4X4 Blue Ox Tow Bar,300 Watts Solar, 2500 Watt '458' Inverter, NO TVs, Most light fixtures upgraded to LEDs