[77newell]

Quoting Richard's Post "In my way of seeing it, if both the brake system and the supply system are leaking down then the massive leak has to be upstream. So Clints suggestion of looking at the air drier blowoff, check valve, and system between the engine air compressor and the first wet tank is logical".

I can't believe I'm going to disagree with Richard, but here goes. YIKES. Given that the air can only flow in one direction from the service tank to each of the brake tanks due to check valves in the lines connecting them, then if there is a leak anywhere upstream of those check valves the pressures in the two brake tanks would remain uneffected. Yes the service tank would deplete, but not the brake tanks. It is true that if there is a leak in the early part of the system (compressor, drier, service tank) AND both check valves are failing to act as check valves then all three tanks would deplete as you have described, that combination of failures just seems unlikely to me.

Yes Brad I was referring to the drain valves on the bottom of the brake tanks, especially if they are the auto drain type like I had failures with.