I use the hole saw bits below to drill drainage holes in a wide variety of items in order to use them as pots. I get mine from Amazon. Search for:
"uxcell 5Pcs 16mm Diamond Coated Hole Saw Drill Bits for Glass Ceramic Tile Marble Rock Porcelain Bottles Pots Brick"
I have several sizes but 90% of the holes I make use the type above.
I should add, you'll need a drill that can accept regular drill bit shafts, not quick connect.
When you're drilling the holes, you'll need to do it while keeping the bit and surface wet. I use an old plastic water bottle with a single hole drilled into the top. I dribble water on the bits and the hole cutting area the entire time it runs.
Remember to let the drill bit do the work and not use excess pressure to speed up the hole completion. A lot of pressure can result in wearing down the cutting edge of the bit and creation of large divets
Start the hole by tilting the drill a slight about to the side. This is the hardest part to hold in place while you get started on the hole. Gradually work the drill back to vertical and the entire circular edge of the bit will make contact and start cutting the hole as a circle. Depending on thickness, it may take 20 secs or 1.5 mins.
The description may sound more complicated than it is. I've drilled everything from thin porcelain to very thick stoneware with these bits. They're well worth the money.
