After much thought, and a minor flood of a freshwater tank in a second floor apartment, I've decided to get my tank drilled instead of using the HOB overflow that came with it. I'm thinking of taking it to one of the stores in town. I've been going to fishy bizness (to look at cool things) and he said he could drill it. Do I need to know where/how many holes I want before I take it there or will they help me decide?