Quote:
Originally Posted by mlh
The in water pressure would haft to drop to zero or actually minus for it to be needed and then only if the black tank was full in the 5 minutes you cleaned the black tank. Now what are the chances of that, a meteor might fall on your head this afternoon but it isn’t likely.
Lynwood
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If the black tank fills up to the point where it is backing up into the toilet, there would be enough pressure due to gravity to push waste water backwards through the sprayer in the tank, and if the air gap/backflow preventer valve was not higher than the toilet rim, waste water could flow up to the valve, and for those that have removed the valve the waste could travel all the way out the tank sprayer inlet in the convenience center. That is one reason for the valve being there.