We study a system of interacting particles in a periodically moving external potential, within the simplest possible
description of paradigmatic symmetric exclusion process on a ring. The model describes diffusion of hardcore
particles where the diffusion dynamics is locally modified at a uniformly moving defect site, mimicking the effect
of the periodically moving external potential. The model, though simple, exhibits remarkably rich features in
particle transport, such as polarity reversal and double peaks in particle current upon variation of defect velocity
and particle density. By tuning these variables, the most efficient transport can be achieved in either direction along
the ring. These features can be understood in terms of a traveling density wave propagating in the system. Our
results could be experimentally tested, e.g., in a system of colloidal particles driven by a moving optical tweezer.