How to drill holes in ceramic pot plants
You need a carbide bit. Keep the surface wet and drill slowly.
Here's a good tutorial for you: https://homeguides.sfgate.com/make-holes-flower-pots-water-run-out-92344.html
Hi Dominique: Here are a couple of sites you need to read before proceeding. I'd also suggest that you get a couple of scrap tiles to practice on:)
You need to use a diamond tip drill bit, and drill slowing adding water to cool the glass.
Put a piece of painters tape where you intend to drill. It will help to keep the piece from cracking.