overflow holes in glass size

[telamont]

Hi,
Im building my own tank with sump plumbed below the main tank. I wanted to know what size the holes need to be drilled into the bottom piece of glass of the tank for the overflow. Is there a couple different standard size options or something? Thanks for the help!

My father and I are glaziers so building this tank will be tough but nothing close to impossible for us.

[uncleof6]

First, all due respect to your craft, however: Glazing and tank building are not remotely related to each other. Perhaps a relationship could be made between materials, glass and silicone. I am certain that as glaziers, you do have a healthy respect for the glass and what it could do to you, if your tank comes apart. :)

To answer your question, what size tank? What flow rate? Why drill the bottom rather than the back? Back drilling is far more efficient in terms of real estate inside the tank, and bottom drilling is something I don't think one should do to themselves.