I use the same as the photo below except all I have is a brass water hose
fitting that's screwed directly to a male air quick connect.
Like the photo with the center stuff missing....
Since my water pressure regulator is typically set at 40 I don't
worry about air pressure more than that.
I usually have a faucet open at all times during the blow out so I don't
even use an air regulator. Just plug on the air hose and stand back.
That open water heater drain has sprayed me too many times!