[Delphinus]

Yep, a glass tank. Drill bit is a diamond-tipped hole saw (cost me about $75 used), and the drill was just a standard variable-speed B&D drill. You use a lubricant and a sort of lubricant reservoir to keep the drill bit and glass from overheating (just have about 1/4" of fluid over the hole), and the trick is to go nice and slow and steady. About 1/4 speed on the drill and just a gentle downward pressure on the drill. Took about 4-5 minutes to pop through to the other side.

I've had to be coached numerous times on the process (thanks Jayson!) in the past, but really, it's not at all bad if you don't mind spending the coin on the drill bit.