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Yes, I guess that would open up the possibility of someone connecting before the PVB and possibly cause me some headaches in my township come time for inspection. "Oh LOOK, I can attach a second garden hose fitting here!".There is a line of thinking that is sometimes reflected in codes, that a blowout valve upstream of a backflow preventer is a cross-connection opportunity. If that is the case in your locality, then you don't see the usual blowout valves in the optimum location at a low point where they can be left open during the winter. This is all relating to above ground backflow preventers fed from a supply pipe exiting the house foundation above grade.
Redundant....Yes, but makes blowing out the system easier. We typically install a "T" fitting below the PVB on the supply line that exits the foundation of the home. Supply line comes into the "T", PVB installed above the "T", and a 3/4" threaded plug on the third side of the "T". By removing the plug in the fall, all the water in the supply line inside the house drains out. Plus, this threaded portion of the "T" gives you your blow out point.