While I was typing this, see you found what you need but indulge me;
OK--look on pg 5.
Dotted lines = cold. Solid = hot. "A12" = adapter on tank outlet to the pump, the first valve (V 10) is the drain, but the arrow points to E 20 (E=elbow), V 10 may be attached to E20, but its hard to tell. OH MAN! Just looked at pg 4 --- Centered Queen bed is same system but with different fittings! Which one should I be looking at? FYI: looks like valve V11 is for anti freeze injection (both pages). On page 4, the hot water tank shows a V11 and V6 which should be the bypass valves so the anti freeze doesn't fill the hot water tank. One more observation on pg 4, upper right (detail C), I see the two V10 valves that are the low point drains I mentioned yesterday, but you are on your own to find them. When you suceed in finding the drain, if you wish, I'll tell you how the anti freeze thing works (you may already know, of course), although I never use it here, and it gets cold!! Tweedy