Air bag drop

The air bags are starting to drop pressure over night, they hold pressure thorught the day I have heard this is a problem with the H2's. I was wondering where the possible issue is I have read it can be the air lines to the compresser to the air bags just wanting to narrow down the scope of things so thought I would ask you all for your idea's.

Usually, the common problem is the air bags themselves. Easy way to check them is get a spray bottle with soapy water and spray it on them and look for air bubbles. If you see bubbles, the air bags are bad. If it was the compressor, the rear would be down all the time