well you couldnt do it that way, if one of those pumps ever failed then you would have a mess on your hands, and the sump skimmers have a pump for just the skimmer itself. you dont have to drill the tank if you get one of those overflow things but they are not fail safe either. best way to go would be to drill it for overflow holes. Look up more info on the plumbing it. its hard to explain it here.