10G tanks are $6.99. Buy a new one!!!
Anyways, the sump is genius. By far the best way to filter an aquarium. So in the back of the tank there is a plastic black wall that has notches in the top for the water to overflow. Two holes are in the back of this chamber one being the intake and one being the out. So essentially when you fill up the tank to the top where the water can start to overflow into this chamber, it fills up to a certain amount and then starts draining into your out pipe down into an external sump. Mine is 19gallons and fits under the main tank on the one side. (I will add a pic later) The dirty water then passes through all kinds of filter media, bio balls, etc and then gets pumped back up through the intake pipe and into the tank. So the level of your tank never drops because you just do top offs into the sump area. You cant even see the filtration one bit when the doors are closed and tank is going.
Plus the benefits are insane with a sump. You gain all of the extra volume, waste and other junk stays in the sump, and there is less maintenance.