I just drilled two holes a week or two ago with a Dremel....it is ridiculously easy. I did it on a 16g tank, for a 1" drain and 1/2" return. If you are interested, I took pictures, I just have not sized them for the internet yet...but could do so this evening.
Here is the thread I learned from though. The instructions are there but the pictures are gone. It is so easy though, it is ridiculous to pay anyone else to do it.
Work the diamond bit up and down (in and out, however you want to describe it), and the glass grinds away smoothly. Going slow, it took me about a half hour per hole.