I feel your pain my friend.... I have replaced the seal to no avail. Mine is obviously not a seal problem. When flushing the toilet the ball valve does not completely close unless you let the foot pedal snap up about three inches from the top. You can move the ball valve with your finger (front to back motion) about 3/4 of an inch... this is not normal, as I have been to RV stores that have my same toilet Dometic 310 and have tried the ball valve in new toilets and they are rock solid with absolutely no movement.
Having researched it to ad nauseaum… I will purchase a new toilet. It has become a pain in the neck and I'm sure folks at least 3 rvs down can hear the loud SNAP each time we flush!!!
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Jeff & Jan - Retired & Full-timing since 2013
2019 Ram Big Horn 3500 Aisin 4x4
2012 Alpine 3450-RL
Double Coin 235/75R-17.5/16 J rated 125lb