Winterizing your irrigation system with a Febco 765-1 Backflow preventer

I found out recently that my new home's irrigation system was installed in the mid-eighties, and it seems most parts (the pex pipes for laterals, the 1" PVC for the run to the valves for four zones, and the backflow preventer itself) were well-built for that time.

Not much has changed—the fittings and main parts of the system are similar to what you can buy today—and the importance of winterizing the system (getting the water out of all the exterior parts) in colder climates has not been diminished!

I have a small 8 gallon 125-psi Central Pneumatic (inexpensive Harbor Freight brand) air compressor; it's not quite pancake-small, but it's no CFM (cubic feet per minute) champion, either. Rather than paying an irrigation company a bit of money to come out and use their monster compressor to blow out my system, I've MacGuyvered the process to get everything cleared out for the past few years. I want to document what I did here for two reasons: one, so I can remember all the steps in the future and avoid a half hour walking between my basement and the outdoor valves, and two, so others in a similar situation can benefit.