Overflow Question

[Maverick00]

that was actually the original plan, however it was a used tank and im unsure what kind of glass im working with. I havent a clue how to 'test' whether or not the back is tempered or able to be drilled. Another problem is i dont have a temp tank i could move everything to in order to drill, i assumed drilling with livestock in the tank would be.. well not recommended to say the least. Looking at the prices of the higher gph cpr overflows im wondering if upgrade time for the tank with panes im able to drill might be the cheaper and better way to go in the long run...