Picked up a 36 Gallon Bowfront aquarium on Craigslist not too long ago and am in the process of setting up my first reef tank. Testing it to make sure there are no leaks or anything, but after it passes the leak test I plan to drill the back glass for a Medium Marine Depot overflow box and a return. Trying to make sure that I can drill the glass as I cannot find anywhere online where people say that they have drilled it. I know that it can be done as long as the back glass is not tempered... the problem is that since it is a used aquarium and i don't have any of the info that came with it, I can't be sure if its tempered or not. I tried the trick using polarized glasses and my computer screen. The front bowfront glass did not ever back out... only showed dark banding. The back glass got very very dim, but i could still faintly see the black typing on the screen. However, I never did see any banding... Would this mean that the back is okay to drill?