The little bleeder screw should look something like the ones below . . . the little black "thingy" next to the big black thingy (the solenoid). You just unscrew those a little bit one zone at a time to open the valve and to blow out that zone. Then close it and do the next one. Seems like it would take forever with a pancake compressor. I used to try to use my 15 gal and that took a looooong time. I found a 33 gal on CL several years ago and that's worked pretty well--has a bit more CFM and a bigger tank.

The process isn't very hard once you do it once. I was kind of intimidated to try it for fear of screwing something up . . . but watched a bunch of videos and it's not hard at all. Just a little time consuming. $35 is a pretty good price it seems these days, so maybe the convenience is worth something.