For an existing antifreeze system without a backflow prevention device, what size hole is required in the check valve separating the supply and the antifreeze?
A 4 in. (102 mm) nominal diameter Schedule 10 sprinkler main is to be supported from the structure utilizing a trapeze hanger with a span of 8 ft (2.4 m). Using Schedule 40 pipe for the trapeze hanger, what is the minimum diameter pipe that should be used?