Well, now I have to report some progress. I tried to attach an air hose, to add a little to one of the tires, and got water out of both the air chuck and the spigot. Turns out that all previous times I had tried that spigot the engine was off. This time it was on, so worked. Further investigation, as a result of the keen ears of my wife "what is that hissing sound?" detected an air leak at one of the fittings on the bottom of the air tank, where it looks like the fitting touched down hard enough to break the hose, but not hard enough to do any obvious damage. Replaced the last compression sleeve, shortened the hose 1/2 in. No more leak. I haven't had time to more thoroughly examine the system, so will report further when I do.