Ventilation holes

[ballpythonsrock2]

Cracks in the plastic from drilling are caused by drilling incorrectly. First what you need to do is mark off where you want the holes to go in a zig-zag pattern like this:
Then you need to get a thick and flat block of wood (preferably at least 1 foot across). It needs to be thick enough that you can't drill through it by accident. Put the tub down on its side over the wood so that one of the places you marked to drill is over the center of the wood. Then you need to drill from the inside of the tub into the wood. Remember to hold down the drill button so that the drill head is moving when you pull it back out.
I hope this makes sense!

I drilled mine and like you say even reaming the drill bit back and forth once in the whole helped make the holes smoother so I had less sanding to do on the edges.
It's been a while since i did it (and the empty tub is sitting behind me with snake supplies in it) but I found if you push into the plastic with the drill running it helped, if you put it on the plastic and then start it will move around (unless you made some nail holes maybe). But I would hold the drill with 2 hands and get an adult to help stabilize the tub or maybe get inside it with your knees to hold it from moving around. Then run the drill and hit the plastic. But be careful above all.

And I did Bogertophis suggestion with the nail, but boy did it hurt when I held the nail. ( Just kidding ) I held the nail with a pliers, it actually worked pretty well if I remember right. I put scotch tape on some of the holes with the edges folded over for easy removal.