I have a Watt anti-siphon sillcock hose bib that spurts through the relief hole continuously when the valve is open and the hose nozzle is off. Is this normal operation for these valves? If not, can I repair it without removing it from the wall? I'm paranoid that I'll damage the copper pipe inside the wall if I put a wrench on the valve. I have no way to know whether its threaded or soldered inside the wall. It also has an outside flange with two screws into the siding.