I've drilled holes in a couple of tanks with no problem but today when I drilled dascos 29 gal tank I was not expecting all 5 sides of the tank to be tempered and it popped and shattered. Whoa, caught me by surprise. Now we all know that 90% of the tanks out there we don't drill the bottom of the tank because the bottoms are tempered. Who would have thought that the side of the 29 was tempered. I drilled another 29 gal tank later, a little gun shy at first but no problem, go figure, Russian roulette.