[Superannuated Peregrinator]

Hello, gurus. I'm the new owner of coach 1223. The compressor has been cycling about every 5 minutes. 

Problem Description
The water collection bowl for what I believe is the air leveling system in the bay just in front of the engine on the passenger side is leaking air. The air is coming from between the metal housing and the plastic bowl at the bottom of the vertical openings in the metal housing as circled in the attached picture. I assume the seal for the drain valve is leaking. There does not appear to be air leaking out the bottom outside the metal housing (air leak detector ordered and on the way), but you can hear and feel the air coming out from the bottom of the open windows in the metal housing where I circled in the picture. 

My Question
Does anyone know how to disassemble the drain valve at the bottom so I can attempt to replace the seal that is leaking? The drain valve spins, but does not unscrew. This is usable as it is, and I don't want to do more damage trying to take it apart until I know how to do it right and fix it.