This replacement filter is built for Petmate Replendish and Mason style gravity waterers and fits units regardless of gallon size. An external layer of polyester material captures hair, debris, and sediment before they reach the water bowl, while an internal charcoal element works to control chlorine levels and reduce odors. Each three-pack includes a filter strap that holds the filter securely in place inside the waterer cap. Before first use, the outer plastic covering should be removed and the filter rinsed under cold water until it runs clear. The rinsed filter is then set flat side up in the cap section, secured with the strap, and the cap is reattached to the filled bottle before it is placed back into the base. Rinsing at each water change helps maintain performance, and the filter is designed to be swapped out periodically as part of routine waterer maintenance.