Air System Questions

[77newell]

My compressed air system leaks down on the supply gauge and the white needle on the 'brake" gauge. Since I have a couple leaks on the rear six-pack I can understand why the supply goes down (assuming the information others have posted that the tank supplying the leveling system is the "supply" tank). Can you tell me which brake tank is feeding the white needle? I suspect the check valve may be leaking so that as the supply tank drains the white needle tank goes with it.

Anything I'm assuming incorrectly here? Thanks in advance

[Neweller]

I would hope our man Forest could answer this question since this was his prize jewel. Not trying to put anyone on the spot.lol!