A pop-up drain assembly for a sink has drain piping, a stopper in the drain piping, a pivot rod for opening and closing the stopper and tends not to clog because the pivot rod is not within a fluid flow path. In one embodiment the stopper has flow diverter plates that channel fluid flowing through the drain piping away from the pivot rod so that hair, waste and debris does not catch on and accumulate on the pivot rod. In another embodiment the stopper and the pivot rod are engaged through magnetic coupling, and the pivot rod does not protrude into the fluid flow path. The stopper is preferably variable in length for adjustment to fit different distances from the pivot rod to the top of the drain piping.