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I clean mine when ever i empty the cup i use a soft bottle brush it's the kind with the sponges i swab the neck cup and body inside and out the pump gets done monthly
Also dont forget to clean the air line. Salt build up and junk will clog it reducing performance. The cup and skimmer neck should be cleaned whenever possible, as junk cakes to the side performance begins to decrease. many skimmers with wipers make this job easy.