I have a couple of these, Camco makes them, sold by most RV places, walmart, etc.
Although I've done it with compressed air, to me it adds another step that isn't necessary. so I simply drain the lines, then flush/fill with pink RV antifreeze. I use about 2 gallons, this includes dumping some into the ptraps and toilet.
I open low point drains and all the faucets, then come back in a few days and pump pink into all the lines. The whole process takes about 15 minutes and I don't need to drag the compressor out.
If you decide to blow the lines out, use one the of brass fittings attached to the city water. Your compressor should have a regulator, set it to about 20-30 psi.
Hook the air line up to the fitting, then start with the farthest faucet, open one faucet at a time, until it starts puffing air. Don't forget the toilet, outside faucets, and the washing machine. When finished, let it sit for a few minutes, then repeat the process.
I would drain my water heater by removing the drain plug, and close the bypass valves.