Waterway Plastics 502-7510 Cartridge Filter, Waterway Top Load, 75 sqft, 2" SlipWaterway Plastics filter model 502-7510 is a 2"s top load filter. For use on portable spas, it is designed to mount in a niche so that the main body is under the shell of the spa, while the top is accessed from above the spa. This complete filter includes a niche lock ring (secures the body to the niche), lid lock ring (secures the lid), 75 sq. ft. cartridge, and lid w/o bromine feeder tube.