A rinse that may be useful to rid your cat of fleas is simply salt water. Be careful of cuts or scratches on the animal’s skin, and avoid eyes and genital areas. Constant brushing of your cat or dog also helps.
But the best cheapest and amazingly useful method is: put a large cut lemon inside a kilogram of well boiled water. Let is sit overnight. The next day sponge your cat’s fur all over and let it remain there. My five cats had this lemon bath for which they did not thank me at all. But two years later I have not found a single flea on any of them.