Using air to flush pipes

Hello:
I want to add two additional sillcocks to my house to help with watering my garden beds. Both of these would be on opposing sides of an attached unheated garage. So, I was going to tap into the current copper pipe that leads to a spigot in the garage and run cvpc pipe to opposite sides of the garage and drill through the wall and attach sillcocks.

But since everything will be unheated in this area I need to flush this section of pipe in the winter. I saw in a plumbing book a recommendation to add a valve(?) that would allow compressed air to be attached and blow out the water. I can't find anything that resembles the recommendation. So, my question is how do you use compressed air to blow out the water in a section of piping. What kind of fixture would I use?
Bob

Not your answer, but a note. If the faucet in the garage is freeze proof, and your pipe bypasses it through the wall there could be problems. If the existing copper pipe runs inside the unconditioned space already, it would not seem to be a problem.

Why not just run the pipe up on the ceiling and fit a valve with a bleed screw lower down? That way you can drain water at one end from the faucets and at the other from the bleed.

It would be about the same as winterizing a lawn sprinkler system. I made and adapter to blow my daughter's yard line. I got a PVC fitting that has male hose threads on one side and male pipe threads on the other. These are 3/4". Next I got a galvanized bushing to reduce the 3/4" to 3/8" female and to that I connected a quick connect air fitting. Connect the adapter to a faucet on one end of the line, open another faucet on the other, open any frost freeze bibs (not sure if this is really necessary, but it won't hurt to be sure, then apply air. Cheap, quick, and easy.

I made my adapter from a collection of parts at home depot. Just hook up the compressor, let the pipe get to 50 psi, open the valve on the other end... repeat.

Looks like this (still attached to a sillcock, from last fall when I winterized the house(oops)):

I'm sure that the 1/4" I.D. of that air coupler will move a huge volume of air and blow out any water in the pipes. LOL

I make a lot of money on poorly done winterizations.
This month the vacation cottages start opening up!

I'd recommend pitching the line to drain dry, and running it in the ever so freeze forgiving PEX tubing.

Been using the same setup as Frenchie for 25 years, on houses and irrigation lines, never a problem.

Frenchie's adapter is identical to mine except I have used PVC hose-to-pipe connector. As far as the air supply size, I blow my sprinkler system with the same size air intake and hose. Other than being a bit slow compared to industrial compressors and hoses, it work just fine.