I want to use a sump for my 180 gallon freshwater tank that I had stopped using. I have looked on the internet to see what is the best way to get the water to the sump. I think as the tank is empty I have settled on drilling the tank as opposed to using a PVC overflow or overflow box. The only thing I need a built of guidance on is where to drill the holes. I am leaning towards the back and need to know where is best place drill the holes...i.e two inches from the side and back?