Most tanks are built with a tempered bottom, and the sides are non-tempered. I have drilled a lot of tanks and it is EASY. All you need is an appropriately sized bit, the tank, and some water for lubrication. The first hole I drilled was on a scrap piece of glass so I could see what would happen when the bit came all the way through (I was concerned about it "grabbing" and cracking around the hole. To start, I start the drill turning slowly dry to score the glass (about 5 seconds), then pour water on it and keep at it. The only pressure I give is the weight of my hand and the drill. About every 20-30 seconds I stop, pour more water on, then boldly forge ahead until you are all the way through. Finally I drink I beer and repeat as necessary.