Geeze, the more I've been looking at some of these installs the more nervous I get about blowing some out. For example, assume that you're looking at a box of electronic valves, not too far away is a DCVA and also a gate valve. No other backflow device down by the meter. No stub for blowing out the system. Question is how would you approach this? Do you shut off the gate valve, hoping that isolates the irrigation system from the house, and then connect up to the last testcock of the backblow? Or, do you hook up to a lateral line via a sprinkler head port, leave that zone's valve open, and then alternate opening and closing other valves? But, perhaps it's not a good idea to blow air back through an open valve, eh? Your thoughts.