[Daryles]

My Thetford toilet leaked, but it leaked from the top of the vacuum breaker valve at the back and only when you slightly depressed the pedal to fill the toilet.
The water did settle around the outside of the bottom making me think the ring was leaking. After checking I discovered the vacuum breaker leak.
I replaced it, not difficult, but working blind behind the toilet, very awkward.
A year later it started leaking again. This time I filled the top vent with roof sealer and taped over it with duct tape. No more leaks.
Why would you need a vacuum breaker behind an open top toilet?
I know, some "code" somewhere.