How to prepare your MAXTRA+ filter cartridge, step by step: Fill your clean BRITA jug with cold water. Immerse the cartridge in cold water, shaking gently to reduce any air bubbles. Insert the cartridge firmly into the funnel until you hear a click. Filter and discard the first two fillings of filtered water. Now your cartridge is ready to filter great tasting water. Tip: MAXTRA+ filter cartridges fit MAXTRA and new BRITA jugs.