Drilling an extra hole

[daplatapus]

It's pretty scary the first time, but actually not that difficult. I usually use plumbers putty, role it in my hands and make a rope with it, and lay it on the glass 1" or so bigger all around the area I'm going to be drilling. Press is down just a bit so it seals up against the glass and fill it with water.
Take your drill (highly recommend a cordless drill) and turn the torque way down. Probably to it's lowest setting or close to it. You should easily, very easily, be able to grab the chuck with one hand and be able to stop the drill. This way if your bit binds in the hole it doesn't grab and break the glass.
I believe the spacing is 2X the hole diameter between holes and/or to the edge of the glass as well.
Hope that helps and if I'm wrong anywhere there, please feel free to correct me