dont drill it. i have tried to drill 3 5o's and they were all temperd. after talking with allglass aka aqion? and perfecto they both said the same thing.. the bottoms are tempered but the backs and sides can be temperd too but they dont mark them. they said they use what ever they have extra as they are a comon tank and sell lots of them. I tried drilling 3 different brand tanks , allglass, perfecto and an old island and same results they all broke and shattered. they were all drilled out the back. i have drilled all size tanks with never an issue but this was my first ever 50/55 and they broke. i wont do it.