Bad Idea! When glass brakes it does not just split. It shatters. If you have a crack already formed, even if you cover over it, the pressure from the water in the tank will continue acting against the glass until its too late. If you don't heed my warning, at very least leave the tank outside filled for a week just to ensure it wont break on you. Water damages in a house can be devastating, I have heard of a 5 gall jug causing 10000$ in damages. Electrical and hardwood flooring. Your better off replacing the tank, or buying 1 pane of glass to replace the entire side.
