[look 171]

See that o-ring (black) like thing up near the top? It goes into a tube (drain) once the pop up is depressed keeping it water tight. Push it again, it pops up above the tube allowing water to drain. Some of that o-ring like flap are clear instead of black. They last for some time.

That thing is no different then the traditional pop up with a lever that goes through a hole in a faucet. That round ball with a shaft through the pop-up traps hair just as fast if not faster