Zelilaa - It should be good for a 5 gallon too, just creates tons of bubbles. I'm using it in a 5 (or 6) gallon tank.
I just noticed though that if you are going to use the water bottle, you should put to other holes beside the hole where you put the end of the water bottle. That way it can come out better and will create a better suction. When I was using the water bottle, the end of it was small so the bubbles would come out of the sides and through the sponge because their wasn't enough space.
But it works great now, I will post a pic soon!
I couldn't fix that on the cool whip container I had because I made too big of a hole, so I used a glad clear container for food with a tight lid and put the three holes next to each other and instead of the sponge, I used a regular filter cartridge.
To put the air tube in, just make sure the end where the air comes out is inside the container. The air that goes through the water bottle (or pipe that the guy used) creates a kind of current and pulls water through the filter cartridge/sponge. It is basically like a sponge filter so it's good with sand too!
If you want a higher current, it probably should be an air pump that's bigger than your tank size. Use a 10 gallon for a 5 gallon.