[prndl]

Originally Posted by DQDick

Just go to most hardware stores and get something like this: https://www.homedepot.com/p/Everbilt...-undefined-_-N

They're required in restaurant mop sinks etc. so they aren't rare.

The model vacuum breaker you show a link to could have a problem. If you ever had a full tank and either stopped quickly or in some other way managed to get fluid in the pipe all the way from the black tank to that particular valve it could siphon into the area you installed it. Especially if your flush line is the same level from the tank to the valve. You will notice the vent (holes) are on the side of the valve that is open to atmosphere and on the side going to the black tank. While you would not get a siphon into the female side of the valve it could be possible to get flow on the male side. That is the reason the OEM vacuum breaker is mounted up much higher than the tank to prevent a siphon from occurring.