I have never used a sponge filter before. It works on the same basic principle as a UGF right? Does the tube stick out above the water line like a UGF?
Yea, what I was thinking was if the tube was above the water line, you could make a hole big enough in the bottom of the trough that the tube could fit through it, but if it's not above the water line, I guess that wouldn't work. The tube for a UGF does go above the water line though, but I have never really liked those much as you shouldn't completly clean the gravel. I guess it's all personal preference.