The additional holes in his setup are for a closed loop setup. Its for additional flow, in place of using regular powerheads. What most people do on the tank you are looking at, or at least what most people SHOULD be doing, is use both existing holes as drains. Then pipe the return from your sump over the edge of the tank if you do not feel comfortable drilling a 3rd hole in your tank. This is called the "herbie" method. It will be quiet and a lot safer than having just one drain pipe. Search the forum for herbie plumbing. I personally do not like the idea of trusting a single drain. I have too much stuff in my living room that i would rather not be sitting in water on the floor.