I have owned a lot of bagged trucks, chasing slow leaks, like when the tank goes empty overnight for example, is a good way to go insane. I started using an engine driven compressor so empty or full, I can leave in about 5 seconds.
on a couple with electric compressors I just put a large ball valve on the tank and turn it off when I get out.
the rule of leaks is: once you have a leak you have an air ride system, and vice versa. keeps me sane!