Just tape the openings in the piupe after removing the PVB. Question, though... 3/4" is rarely used and only allows 8-10 gpm through. Curious why this was chosen as size pipe.
Uhhh, you do realize that backflow preventers are rated for the same flows as equivalent water meters. That means a one-inch PVB is rated for 50 gpm, not that anyone would plan for that flow.
I'm assuming he's refering to the pipe size, not the size of the backflow preventer. Of course 8-10 gpm in a 3/4" pipe is going to put you more towards 7fps rather than the 5fps limit suggested now-a-days. So for 3/4" pipe, the design flow should be more around 6-7 gpm.
Then again, the OP didn't say anything about the pipes for the rest of the system, just what is at the PVB. I know that my water supply is via a 3/4" meter, but the pipe just past it is 1" PVC.