My pump has quick connect fittings, so I made up a quick connect with short tube to go from the antifreeze jug to the intake side f the pump.
Drain water heater, bypass, open all faucets, drain low point drains, close everything and allow the pump to pressurize system with antifreeze, run faucets, toilet, showers, etc.. Making sure pink flows and fills traps.
I have no doubt the air pressure method works, I am just not brave enough. I would probably use this method if I needed to use my trailer in the winter season more than once or twice. As it is we usually only head out for thanksgiving.