Foam filter replacement inserts for the Dogit Design Fresh and Clear Large Dog Drinking Fountain. Each of the packages contains 1 small foam insert and 1 large foam insert. Make sure your dog always has access to plenty of fresh-tasting, cool, filtered water. The foam filters trap debris and absorb impurities for cleaner water. Foam Filter and Foam Insert should be replaced every 6 months. More frequent changes may be necessary due to indoor environmental and water conditions, as well as multiple pet use.