Dometic toilet burping
Working on dad's 5th wheel Dometic toilet. Recently replaced original toilet with new 310. All well for abt two weeks. Now, on about half of the flushes, it burps, which has unpleasant consequences!
Have read many blogs on this issue and have done the following, on the advice of said blogs:
Tank flushed multiple times till water runs clear;
Gallons of hot, boiling water poured down toilet;
Ran snake and water sprayer down toilet;
Ran water down the roof vent pipe, with no evidence of it filling up;
Can hear water running in that pipe from on the roof, when toilet flushed;
Snaked the dump line;
Ran the black tank flush line for over an hour, multiple times.
Only thing one person mentioned was possibly a defective anti-siphon valve, which I can't see how that could have any relationship to the burp, based on what the purpose of that valve is.
I'm out of ideas! Any thoughts would be appreciated.