The present application includes and assembly having a hollowed body configured to traverse the length of a well bore and remove contaminants. The hollowed body having an upper seal body and a lower seal body. Each body including a seat for securing and sealing by a dart. The dart is configured to transition between the seats by passing through a central channel of the hollowed body. The dart includes a central passage and an unobstructed lower passage in the tip of the dart to allow for the direct passage of working fluid. The assembly further includes an expandable seal configured to expand in diameter from the increase in pressure in the well bore. The expandable seal contacts the walls of the well bore. The expandable seal cleans the walls of the well bore and prevents leakage of working fluid between the walls and the assembly.