That might work on an air over water type tank, whci his very rare today, but on a captive air precharged tank, it will blow the bladder. That's if I'm understanding what you are saying to do.
When he drains his tank, the air pressure forces all the water in the tank out of the drain. The drain valve will also allow draining back his plumbing that is capable of draining IF he doesn't have the water shut off past the pressure tank. Now connecting a compressor to a faucet above the pressure tank will blow the water back to the drain on his tank. But may still leave water to freeze in some areas of his water line plumbing. Usually draining gets it all but in some cases it won't in a piece of pipe here or there; like those not going trough a beam and going under it and back up. Water will be trapped in the belly part.
Connecting the compressor past the water shut off valve for the house and opening each faucet/fixture individually and then all of them should do it. Then leave all the fixtures open until spring.
Gary
Quality Water Associates