I've never drilled glass. Switched over to almost all acrylic tanks. The Gl*******s guys make it look easy though...LOL You could always go with acrlic for the sump. Just buy the first thing you can find on Craigs list.... Or even a rubbermaid... Not a tote but like an ag vat....... But it would be kinda ugly/hard to hide.
Are you dead set on using a glass tank as a sump?
Are you dead set on using a glass tank as a sump?