I learned the glass drilling from (I think it was) Turning Tim?....but he suggested using a "Rotozip" (brand name for a dremel type rotary tool) "tile bit" used for cutting standard floor and wall tile. these bits are about $11 or so at the big orange home fix it up store....hanging with or near the dremel bits...they fit also in standard dremels. you need to lubricate the cutting surface (the actual hole you are cutting) continually with water so that it doesn't overheat and crack. With this tank, I pumped water over the cutting area through tubing taped strategically on the side of the tank in order to direct water flow over the cutting area. In a later tank I simply put a bucket of water up on a lader, and using airling tubing used gravity to irrigate the cutting area. On this other tank I held the airline tubing in my left hand and aimed it so water flowed continuously over my cutting surface, while I held the dremel with my right hand and did the cutting.....(I always seem to have to work alone which always complicates things) If you have someone else around to help they can take care of the water while you do the cutting.
the other thing you can do is go online and buy a diamond hole cutting drill bit...but they are alot more expensive $50-$100 a bit. they will cut a cleaner hole for you if you can handle a heavy drill. you still need to lubricate/irrigate the cutting surface with water....This was a bit awkward for me...I wasn't sure I would be able to easily manage this much heavier piece of equipment, so I opted instead to use the smaller (and ultimately cheaper route) the dremel and "tile bit"
