I cracked about 4 10g tanks before I finally got the hang of it. The smaller tanks like that are harder to drill because the thin glass cracks really easy. I finally figured out that you need to put almost no pressure on the bit and take extra time drilling thinner tanks like that, and it can be done. Be especially gentle when you get ready to break through the other side, as this is when it cracks. I never use the antifreeze and the round barriers to keep the water in, like some people recommend. I've found that it wrks fine to just have a cup of water handy and make sure the bit always has some water around the base as it is cutting. I definitely prefer to use a drill press, as it gives a more level cut and is easier to control the pressure on the bit.
Forgot to mention, there is some guy on Ebay that sells diamond hole saws really cheap. That is what I use. Some people were skeptical as to whether they were good enough quality to drill multiple tanks, but so far I have drilled about 10 tanks with one of the bits I have, and it still seems to work well.
