The filter sleeve is a form fitted felt filter bag. The 5 micron sleeve slides over the outer portion of the Outback’s primary filter. The sleeve acts as a second stage of filtration helping to capture smaller unwanted sediment particles that may be present in the untreated water supply. The sleeve is held in place with the FDA approved elastic band (included). It is recommended that once the sleeve is clogged or shows sign of a diminished flow it is best to replace it rather than attempting to clean it.