A pump assembly for a dental cleaning appliance includes a fluid chamber, a piston, and a drive. Magnets, connected respectively to the piston and the drive, enable the drive to couple to the piston and move it within the fluid chamber to draw fluid into the fluid chamber. A stop prevents the piston from being pulled beyond a stop position so that through continued actuation of the drive the magnets separate to allow a spring to push the piston away from the stop position to urge a burst of fluid from the fluid chamber.