The Inline GAC Filter is a post filter. Inline GAC Filter uses granular activated carbon. The carbon filter absorbs impurities and removes chlorine taste and odor from your water. Filter fits 1/4" female pipe thread. Installation is quick and easy with the water directional flow arrow printed directly on the filter cartridge. It is recommended to flush the water line after installation to remove loose carbon particles. Generally, this filter is replaced every 12 months to assure quality of water.