Very easy and cheap way to make your own Aquarium sponge pump. Perfect pump for small tank, small fishes, shrimp tank, breeding tank ... Using a simple air pump and basic materials, you can create a mechanical/chemical filter for your aquarium!
Sorry for my very poor drawing, but the idea is there!
When air goes out of the air tube and up the wider tube, it sucks up water at the same time, so water goes through the sponge, up the tube and clean water comes out.
As simple as that!
The sponge serves as a mechanical filter holding big particles in it, and also as a bio-chemical filter. Good bacteria will grow in the sponge and clean the nasty stuff out of the water. You only need to wash the sponge with clean water from time to time.