Airtight-ness - While it is always a good thing to have an airtight piece, if you can manage to get enough air to dilute but not too much to loose suction then your hits will be excellent.

Drilling glass - mason bits are said to work if you cant afford the diamond ones. if you dont have any of that shit than start with a very small bit and drill very very slowly. I've been able to drill through but its really tricky and not worth breaking a kick-ass bottle.