If the planter isn't sealed, you don't even have to have the drainage holes as the tufa is porous which is why they make super planters, but if you want them, I've used just regular drill bits....go slow though, so nothing 'chips' off.
Marcia

Use a masonary drill bit not a "regular" drill bit. It's meant for masonary work and will hold up much longer.

Marcia, don't know what recipe you use. My planters/troughs are porous but if the drainholes get clogged the container will hold water. Billie

I don't seal my tufa planters, and I don't sift the peat at all. My sedums, ( if I spelled that right,) are always dry (no drain holes). My biggest is about 11 deep and 24 inches wide inside, and I planted geraniums in it last year. I had to water every day, that has drain holes in it. And I have some cheap drill bits, just regular ones, and every once in a while I just file the edges. I guess masonary bits would be better, but just never bothered.
Maybe - thinking back...I didn't pack as tight....I haven't planted the ones I made where I packed the sides down with a piece of wood and really tamped it in. I was going to try to sell them off this fall when I have my annual garage sale.
Marcia

I have never put drainage holes in any of my projects. I've had sedums and herbs in some of my pots for years, and never had a drainage hole.