I've made plenty, as they say a picture is worth a thousand;
Pepsi can is for size reference, it's not part of the filter. I put a bit of gravel down the lift tube for weight, sponge is open cell found at a local shop.
Simple, effective, and cheap. These have been the secret (or not so secret) of breeders for years. Squeezing a dirty sponge from a mature filter will seed a sponge filter. Be sure to continue a fish less cycle afterwards to ensure you get a good strong culture going.