[johnkosir]

I agree with Richard the reason I have shut off valves on every line coming off my tanks is because I have a small leak I can not find. I would do it a little different when I had the line off to put in the shut off valve I would put my bubbler in series with the tank and I could see how much air is going down that line. you could also just use a gauge put air pressure in the line, turn off the valve which is between the compressor and the gauge  and watch the gauge where your big leak is the air pressure will drop real fast, I would also figure out where the line goes and mark it. then do the next one.