I have a question about chest tubes... With the Pleur-Evac system, how should the Air Leak Meter look when the system is functioning properly? I keep reading that if there is bubbling from 0-7 there is an air leak Please define bubbling? Does this mean if the 0-7 columns fill with the water or does this mean you actually see the fluid bubbling? Should there be water in the 0-7 columns normally? I am just confused....