Is that 40 psi with all the taps open, closed or what? I am guessing you set the compressor to 40 psi max, then it goes down to 2 or 3 psi when a tap is open - and a tap should always be open while winterizing so the air is flowing fast enough to carry away water in the bottoms of the pipes. Being liquid, antifreeze doesn’t need to flow fast to push water.
I use a gallon of antifreeze every fall, then buy for next year when it is on sale. We carry our drinking water in two jugs so we never taste antifreeze residue and don’t need to use bleach in the water system.
I prefer the antifreeze method because we sometimes get camping weather in Winter but need to be able to winterize when it turns cold again. Nice to just carry a jug of pink stuff instead of a compressor. And winterize in half an hour.