The act of placing your genitals within sufficient proximity to the filter jet which circulates the water in a pool in order to pleasureone's self.
Jeff hasn't moved from that spot along the side of the pool in over ten minutes, he must be filterbating. Filterbation is best accomplished when no one else is around...
Boys who enjoy yaoi (a genre in Japan that contains sexual and/or romantic relations between two men); literally translates to "rotten boy"; corresponding female : fujoshi