Just got a 75g recently and am going to get it drilled on Friday. I'm going to run the drain through the rear (as the bottom is tempered) hopefully as an external durso set up. It is going down to a 40b that will be filled with lava rock for bio media and use a mag5 (that I already own) as a return pump. I guess my first question is with the return, how do I plumb the return back to the tank? I wanted to do a spray bar so do I just run it over the rim of the tank? Also how do I decide where the drain hole is drilled is there some type of calculation? Will having an external durso set my water level to low, do I have other options? I see so many things about sumps and I'm just plain old confused.