Followup question (maybe this should be a different thread but) - the tank I'm using for my new sump I got for free. It's a 40B, but it has a very thin, but very long crack at one end between two drilled holes. I will not be using the holes, so to mend the crack and cover the holes, I planned on just throwing a piece of acrylic on the outside of the tank covering the entire side, sealing it up on the outside. Then, when hardened - sealing up the holes on the inside and running a bead up the crack.
Is there a better way? The crack is really tight and the tank will only be half full (or half empty depending on your self esteem) so I don't think it's a huge deal, especially for a free tank, but I want to make sure I seal it the best way possible.