Replacement cartridge for Battery Watering Technology's Water Deionizer (PW-1800). Filter Cartridge Replacement: 1. Turn off water supply. Press red pressure-relief button (if present). 2. Unscrew housing. Remove large o-ring, wipe clean, and set aside. 3. Discard used filter cartridge. Wash housing with dish soap and warm water using a non-abrasive sponge or cloth. Rinse thoroughly. Fill 1/3 with water. Add about 1 tablespoon of bleach and scrub to disinfect. Rinse thoroughly. 4. Lubricate o-ring with clean silicone grease. Insert o-ring in groove. NOTE: This step is important to ensure a proper housing seal. Make certain the o-ring is seated level in the groove. 5. Insert new filter cartridge making sure the top is facing up as indicated. 6. Screw housing onto the cap and hand-tighten. Do not over-tighten. Make sure cap standpipe slips into cartridge. 7. Turn on water supply. Press pressure-relief button to vent excess air (if present). Check for leaks before leaving installation.