I don't remember the exact type, but I'll check when I get home. Fluval makes a type of filter sponge that's white and comes in long rectangles. I just cut part of it off and stuff it into the filter outlet. I have two tanks set up this way. Just leave part of the filter outlet unobstructed so the filter doesn't overflow, if that makes sense. Basically, find a sponge that will fit and stuff it into the outlet, but not too tightly. My water is almost completely still on the surface but tons of filtration going on.
I can show pics later if anyone's interested. I can take pics when I get home.