You don't have to drill the sump to use an external pump. I didn't. I just used PVC and a couple of elbows to loop over the top of the sump and connected it to the suction side of the pump. You can even use tygon tubing to get away from the elbows if you have some way to anchor the tygon where you want it in the sump. A chunk of live rock and some wire ties comes to mind as one possible solution.