Diamond Tipped Hole Saw, you‘ll need a Jig to keep it in the Right position. In the past, I used a piece of plywood cut to go against the glass on two sides, and drill a hole in the Plywood with a Standard wood/steel Hole saw. They now have adjustable plastic guides. Also I used 50/50 Antifreeze as the Lubricant/Coolant. Go slow, let the weight of the drill and bit do the work. Once you get a groove cut, you can use plumber‘s putty to keep the lubricant around the drill.