As requested, here's my method for venting clay pots that don't have enough holes in them to make orchids happy. Safety first, please wear safety glasses when you are using any cutting tool, and there will be terra cotta dust, so if you don't want to breathe it, a fiber mask would be in order as well. I did my cutting in front of a window in my DH's shop and there was a nice obliging breeze blowing the dust all over the floor instead of into my face . . .. in hindsight, the little shop vac would take away the dust very nicely (but it makes such a racket!).
I use a Dremel tool with a little diamond wheel on it. You may have to use a larger wheel if you have a bigger, thicker walled pot. My pots are only a bit over 1/8in or 2 to 3mm thick. You also are pretty much stuck with straight-sided holes, because the wheel only cuts straight cuts. It would take a lot of time and patience to make anything like a curved cut.
These two little clay pots came with dying phals in them, from the Lowe's death rack. No wonder, the clay pots had no holes whatsoever, and inside each had a plastic pot as well. Soggy moss, hello-o! You can see my first attempt at a square hole in the bottom of the pot was not very tidy. I've improved my technique since then. The wheel cuts best if the clay is dry. Moist clay will gum up the wheel and you'll need to rinse it off during the operation.
Turn on the tool, I use speed setting 7 (the tool has 1 to 10) and very light pressure to keep the tool, wheel and pot from overheating. The clay is not hard, but it is fairly dense. If you see sparks where the wheel is cutting, you are pressing too hard. Don't try to go fast, it only takes about 30sec. to make each cut. If your Dremel tool starts to get hot, stop and have a cup of tea while it cools down.
I like to make little slanted rectangles (parallellograms) for those of you who are into math. So I cut two parallel sides about 1/4in. apart. Then I make the end cuts to break out the piece on the inside of the pot because then you don't see the extra cuts.
You can make squares or triangles (see below) rectangles, or star shapes, whatever turns your crank. Don't make the holes too big, though, or your bark mix or other medium will escape out the holes. Hmm, star shapes would be fun for gift pots at the holidays . . . I think I'd draw the star in pencil on the pot first, rather than try to freehand it. Or make a little pattern.