I assume you have an overflow HOB? If so the air tubing into it is just to suck the air out. Once you remove the air then remove the tubing. To have less trouble with this, drill a small hole into the top of the box where the air accumulates, and put a one way valve on it. put some air tubing on it just to control where the air goes. Another step in the right direction is to jimmy-rig the air tubing, from the valve, to a powerhead on its intake. This way the powerhead will suck the air out of the overflow. These steps are not fool-proof, but they will limit your number of problems.