Placement and size of overflow holes?

[haha]

Im about to have my 40 gallon breeder drilled by a local shop. I need to know how many holes to drill, what size the holes should be, and where they should by placed. Thanks.

 

[Northstar24]

I am not sure on the size, but I think the standard for AGA aquariums is 1 inch for the drain holes

Most pre- drilled aquariums have holes drilled the back corners of the tank, but I have also seem both on one of the short sides of the aquarium but that was for a in wall set up. I would think you would want one on the back wall in each corner