I just got a new sponge filter just to supplement my HOBS. I just don't get how they work? The air stone is connected down in the intake part which is in the sponge and it makes bubbles come up from the tubing, so how does it draw INTO the sponge if air is being pushed OUT from the air pump?
Does what I'm asking make any sense? It's hard putting it into words.

The air bubbles rising out of the top of the tubing creates a low pressure area in the water. Because of physics, the water flows through the sponge into this low pressure area and out of the tubing on the top of the filter.

I knew there had be a good answer to it! Thanks

Bak2it is the guru of these matters! Ask a physics question and he'll answer every time. It's great to have his advice here!

I know....I knew when I was posting that he would help me out!
Thanks Bak2it!