drilling a tank

[monocus]

just make sure when you drill that you go slowly and let the weight of the drill be the only pressure on the tank.when i drilled my 220 it took about 1/2 hour-40 min.

[Proteus]

Set the clutch on your drill. This will eliminate cracking from torque. Also slowly rock bit as not to drill level

[BlueWorldAquatic]

Make sure the glass ins't tempered, use a set of polarized glasses (fishing glasses) to see if it is.

slow and steady, with water for lubrication. Doest hurt having some wood clamped on the other side to reduce chipping also.