Yesterday I made a filter for a shrimp breeding tank out of a small plastic water bottle.
I made some holes in the side near the bottom of the bottle. I had a aquaclear coarse sponge and cut a square the same size as the diameter of the water bottle. I cut a slit across the bottom of the bottle, and put the sponge about in the middle of the bottle. Then I put a rock (to weigh it down) and some poly-fill below the sponge.
I made two holes in the cap for the airlines, then cut a short piece of airline, about 4", from a section of airline that had a curl to it and put it in the cap so that it sticks out the top and curls over (and doesn't extend very far into the bottle, maybe 1/8" - 1/4"). This pulls water through as the air bubbles up through it. You can use a bit larger size of vinyl tubing for this part if you need more flow, I just used airline since it's all I had.
Then I put the other airline through the cap, attached a small airstone that drops down into the bottle and sits on top of the sponge. The other end attaches to the pump, of course. I put the airstone in first, then added some established ceramic bio-media (biomax) on top of the airstone. Now I have an instantly cycled shrimp tank to start breeding RCS.