The Katelyn gravity replacement element 20720 is a replacement Filter for the Katelyn trk Drip gravity system. 3 filters needed for the Katelyn trk Drip gravity system. The Katelyn gravity 20720 elements have carbon inside them which eliminates odors and chemicals in water. The Filter can be cleaned multiple times before a replacement is necessary. The Katelyn gravity dual filtration element for the Drip offers Ceramic and activated carbon filtration.