Good news is, my BT does not back up.
But the BWT does build up pressure and bubbles come back through the toilet valve and when flushed it burbs the water in the bowl (nice splash).
I am thinking it might be the vent pipe, blocked or to long into the tank.
The other big one was the BWT flush system, does not seem to work.
Did you figure that one out?
Did you have any problems with your slides closed? Mine seem like they have a large gap 1". It almost looks like aliment or oversized gaskets.
Any info on those items would be great.
Thx