if your tank is not tempered glass then it is no problem to dril it. as for why drilled is better, it really is something that needs to be experienced before you can truely understand. I myself was told drilled was better , said it can't make that much of the difference, and bought the non drilled 135, after i got the drilled 65 (was on sale and i needed to shove it into a corner) Man life is SOOOOOOOO much easier. no annoying space behind the tank, no tubes running over the back of the tank to clog with algea. I sealed the 65 so no escapees. Drilled is a wonderful thing. can not stress it enough.