My 75 is drilled. I absolutely love having a sump. I made it by splitting a 35 using plexiglass dividers siliconed in. The water dumps into a open area, then down through 5 layers of filter media, then up through 5 lbs. of lava rocks, then down over charcoal, then to the return pump. I also have a 5 gallon pal tied to it with tubing and a float valve for automatic top off. It increases water volume and airation.