tko, When you say use the lower of the two drain valves, are you referring to the lower of the 2 testcocks on the actual Feblo backflow unit, or a drain spigot downstream of the backflow unit? I have a Feblo 765, with the same basic setup as the picture DavidQ posted, but I do not have an drain valve downstream of my backflow unit...just one upstream (in my basement). It seems like I have a non-standard setup, but I'd like to learn to winterize my system myself. I have a powerful air compressor,...