John,
No such thing as a dumb question, just sometimes dumb answers.
I really don't know if it matters, but I have always have air in the bags because of having to reach past the front tires and it is easier when they are inflated and suspension is up.
You really don't deflate the air completely when blowing down to remove the water from the tanks.
The three tanks are 1 for front suspension air, 1 for rear suspension air and 1 for the air brake air, that is why there is three cables connected to a valve for each tank.
Ron