I run compressed air through my lines and pump, not a great deal of pressure, I think the pressure gauge on the pump usually will show 30 to 40 pounds of pressure while its blowing.......I have done this for years and so far, so good.
Start by pulling the pick up line out of the fill hole in the top of the tank, unscrew the screen on the end of the rubber pick up line and then run the air pressure through the pick up line to clear the spray nozzles on the back of the frame. Then, turn the control valve and make sure the spray hose valve is opened and continue.
After all, if I am trusting my 16 zone lawn irrigation system with 148 spray heads and over 6,000 feet of poly pipe to being winterized with compressed air, the same should be adequate for my 45 gallon sprayer tank......and it always has been so far......(for both the irrigation and the sprayer)...........