Backyard Aquaponics
A place to discuss aquaponics

I used a hot knife. It was like cutting butter and I got the holes I needed easily. But I think it would have been faster if you get a round metal cookie cutter the size you need and heat it and just press it through.

I used a fostner bit, but my drain are small (1").

I used a hole saw. A 3.25" hole is needed for a 2" shower drain.Some drains take a lot of extra clearance. The 300-gallon have a nice big space between the waffles, in a nice location near the edge.
The 100s feature smaller waffles, need some "waffle wall" cut to allow a big flange, fitting or drain. I think those are best drilled in the side the way TCLynx does.
Measure thrice would be my advice in any tub. Find the flattest area you can.

Rick

There is a lot of blue and white plastic barrels that get 3/4 inch pipe fittings. It is easy to drill a 7/8 inch hole and use a 3/4 male pipe thread tap to make threads. That makes a hole that wont leak and be without all that sticky stuff that takes an over night wait to check for leaks. Just screw in the fittings and done.
Don

Lot of nice suggestions here. I have to say I am glad I read this topic as I was wondering the best way to make a hole in my first GB.

I've had good luck with a hole saw intended for wood, running the drill in reverse for poli or plastic.