To cut off a bad faucet vacuum breaker with a saw, follow these steps:
Use a hacksaw or reciprocating saw to cut the vacuum breaker just below the threads.
Be careful not to cut into the faucet itself.
Once the vacuum breaker is cut off, remove it by turning it counterclockwise.
Apply a thin layer of plumber’s tape to the threads of the new vacuum breaker.
Screw the new vacuum breaker onto the faucet by turning it clockwise.
Turn on the water supply to the faucet and check for leaks.
Wear safety glasses to protect your eyes from flying debris.
Make sure the saw blade is sharp and in good condition.