Cleaning balls are super handy for scrubbing the inside of your transfer tubing. Simply insert into the end of the suction-side tubing connected to your pump and turn the pump on. Be careful not to draw the ball in to the pump head. For the outlet side of the pump, disconnect the tubing from the pump, insert the ball, reattach and turn on the pump. for best results repeat several times on each side. If stains persist, fill your lines with a warm PBW solution and let sit for about an hour before scrubbing again.