I just had a plumber put in a backflow for me, they put in a Watts 800. They put the connection for winterization upstream of the PVB, and said that we can just blow out the system through the PVB to winterize. They said "they just did a 1.4 million dollar home and they always do it this way". I was under the impression that I should have a blowout tap after the downstream valve of the pvb, then I could hook up the air there and blow the system out with the downstream valve closed, so the air doesn't blow through the PVB. Who was right?