Be a man...drill ur own tank. Depending on how used the diamond bit is, I would use a fresh diamond drill bit, they are not expensive. Sometimes used diamond drill bits, are worn of diamond and might not cut as well...and increase the chance of breaks/chips.
- Just take it really slow. Use lots of water.
- Let the drill bit do all the work... Don't press down... Remember u are grinding glass down, not cutting a hole like with wood...
- Use a pre cut styrofoam hole template as an initial guide to get it started.
- Have a cushion under to catch the glass, when the hole is complete..