Get a jar like a peanut butter jar or small 3-6 ounce jar of some sort, stuff it full of filter floss (polyester filter fiber or some sort of material. Cut a hole through the lid (weigh the inside of the jar with some rocks and hide it behind a plant or something) put the tube underneith all of whatever you filled the jar with and the co2 tubing through the lid of the jar, punch holes in the lid of the jar for the co2 to escape and there ya go. I also once heard of people putting a "umbrella" shaped piece of plastic over top of the co2 output tube to catch a reservoir of co2 before it bubbles and floats to the surface. However I don't think the 2nd one is very effective.