Lots of people blow out their pipes through the city water fill port, so I bought an adapter and did mine at 40 psi. It did blow out the water but it also blew out the check valve.
Now, I open the water faucets, remove the hot water plug, open the fresh tank valve and open the low point drains.
The next day I set the water heater bypass valves. Close the low point drains and pump antifreeze through the water pump inlet. I bought the tubing and pump connections in the farm store's sprayer section.
It takes two gallons of antifreeze and an extra gallon for the P traps. I flush each faucet separately. The entire process takes 20 minute, not counting the overnight drain.