I bought one of those diamond coated hole saws from "oksupplies" on ebay and drilled a 10 gallon tank this evening.

Making a suitable jig to hold and clamp the tank took longer than drilling itself. Doused the area with water before starting - didn't heat up whatsoever.

A 10 gallon tank is only - what - 1/8" thick, but getting a good hold (but not too tight), going slow and keeping cool proved no hassle.

I'm gonna use two 10 gallon tanks as a split fuge and sump/return for a 30 gal hex seahorse tank.

The 10's fit in the nearby cabinet without altering. I figured at $10/tank I'd have to find different reason to build a custom acrylic tank.