Genuine Merrill P-115 plunger. The plunger is designed to go down into the valve body, and keep any water from leaking out of the hydrant. The Merrill P-115 plunger has a set of metal threads that are surrounded by a hard rubber. The rubber of the plunger is what creates the seal in the valve body. The P-115 is designed for the Merrill WM2000, and M2000 yard hydrants.