I'd like to connect an "anti siphon" valve outside the house just before my 3/4 pipe goes to the valves. I'd like this "anti siphon" valve to have a "port" where I can connect my compressor to "blow out" the lines. where can I get such a thing? or is there some other way to get some air in? I want to "blow out" each zone including valve so there is no water in there to freeze.