plunger
plung.er \'pl*n-j*r\ n : one that plunges : as : DIVER : a reckless gambler or speculator : the rod carrying the valves in the inner assembly of an automobile tire valve unit : a sliding reciprocating piece driven by or against fluid pressure; esp : PISTON : a piece with a motion more or less like that of a ram or piston : a rubber suction cup on a handle used to free plumbing traps and waste outlets of obstructions