I just finished winterizing with my 5 gallon AC. I set it to 50 psi, connected using an air adapter on the water inlet. The adapter only has a 1/16 inch hole to prevent ripping the piping and rubber seats on the taps with excess air volumes. I bypassed the water heater, drained it and opened low point drains. I previously drained the water tank. Using the air I blew out the low points and then closed them and blew out taps, shower and toilet (remember the spray head). Set the water pump to draw air from the antifreeze connection, made sure the filter was drained and ran the pump for a few seconds til I could be sure it wasn't pushing any water. Then I opened the low points and blew them out again. Left all the taps and low points open. ...done in less than 30 minutes including running hose from the basement where the AC is located.
Last thing was to pour a cup of antifreeze into each trap and about a quart into the Black Water tank via the toilet.
The trick as noted many times above is to let the pressure build up then open a tap on Hot; repeat on Cold. 50 psi was plenty. I have actually done this using a 12V
compressor in the past...just takes a litter longer.