PRV on black tank flush

[Haonkered]

Is it necessary to use prv on black tank flush? Also I dont even see on my owners manual where I need a prv on city water connection but dealer told me to use one and boy does the pressure suck!!

[sherdep]

PRV?
Pressure regulator valve?
what pressure is the one you are using 40 to 45 or 50 to 55 psi?
I do not use one on my tank flush
I do use a back flow preventer though

[wayne anthony]

According to what I found on google, the vacuum breaker valve needs 40 psi to open.