Slang referring to an aggressive, furious, rapid act of fellatio. The piston pump receives its name from the rapid head movement exhibited by the provider of the fellatio, which is said to resemble the action of a moving piston. This is also referred to as the jackhammer. The piston pump is much sought after in the world of fellatio and should be received with grace and humility.
Man, that piston pump was great. I have never been sucked off so furiously.