Uh - are you sure that's an acrylic tank?
The tank is glass. There's a heat-shaped piece of acrylic I'm using to separate land from water, and I wanted to find the best way to adhere silicone to glass so that it will hold water - there seem to be a lot of mixed opinions about that. But that's the reference to acrylic.
Thanks for the glass drilling advice, it makes me less nervous about breaking my tank. I have a decent amount of construction experience, so I'll go slow and let the bit do the work. Only difference is I'll be drilling the back, not the bottom, since the last tank I had drained through the bottom and it was hard to move with a piece of pipe sticking out of the bottom.