[jeffba]

Originally Posted by rohrmann

The instructions for these valves say they are supposed to be installed higher than the top of the rim of the toilet bowl so the water has to run back to the black tank on that side and back to the water inlet on that side. That’s why they are either placed way high under the bathroom sink or up high behind the shower wall, to help prevent the siphoning.

The same reason why my anti-siphon valve has to be higher than any sprinkler head for my S&B sprinkler system