If I were in your shoes (and I have been), I'd go the soldering iron route. When I tried making holes with a drill it either 1) cracked the tub, or 2) made a rough edge that required smoothing out afterwards. The soldering iron made a nice clean hole in a fraction of the time.

If you don't already have one, you can probably find a soldering iron in the $10 range at a local hardware store that will do the trick. Just make sure to do your hole punching in a very well ventilated area. I did mine outside and the fumes were still pretty noticeable.