You need both a pump and a filter. The filter you can make yourself. I use a large storage bin or garbage can. I put like a laundry basket inside . Inside of that I put a mesh clothes bag with polyester stuffing and pantyhose with activated charcoal in it. The pump sucks out dirty water, which goes into the filter. I set the filter by the side of the pond, and put holes up high for water to flow out. Or you can use PVC pipe if you want to hide it somewhere.:-D