The answer depends on the flusher.
Model: The Flusher: (yes that's a model) is nothing more than a sprinkler head, the backflow device is "up-line" from it and is a vacuum breaker that is mounted ASBOVE the top of the tank.
Model: Tornado: Has a spring check vlave in the flush head itself.
others: Vary.
Recommendation: You must likely have one like "The Flusher" from the factory, Replace with Tornado, i did.
Recommendation 2: I feed the Tornado via the original vacuum breaker, PLUS a 2nd Spring check and vacuum breaker on the supply hose.. Belt and Suspenders. 2 sets. Am I paranoid.... Well when I "Bult" the hose I did not knwo about the existing back flow preventers so no. Not that much.
Oh, and I use a Quick Disconnect so when not flushing, Hose is disconnected (At the moment it is connected to a hand sprayer).
