Here Stops The Leak PRO53 PRO54 PRO55 Fluidmaster offers the only line of Flappers Exclusive to PRO’s PRO56 PRO58 FOR 2014! DID YOU KNOW ? NEW FOR 2014! NEW Built-In Fluidmaster PRO Series flappers made with Microban ® technology are more resistant to premature deterioration than other flappers. The Microban additive operates at the cellular level to prevent uncontrolled growth of microorganisms that can damage the flapper.