Drilling Glass With a Dremel

[viperfish]

So here's the scenario; I have a 20 long that I want to set up as a water change tank. My plan is to drill a 1/2" hole through the glass and install a float valve in the tank. I am going to tee into the line to my top off reservoir so my RO/DI feeds water to the W/C tank. I just figured in the arsenal of attachments in the Dremel kit (90% of which I never use) there should be something there that could poke a 1/2" hole in glass. Anyone ever tried this? Which bit works best?