THE FILTER RUNS BY GRAVITY.. ITS LIKE THE REVERSE OF A WET/DRY BEING UNDER YOUR TANK. THE PUMP IS IN THE POND PUSHING WATER INTO THE TANK. THEN THE WATER RUNS THROUGH SPRAY BARS AND AND DOWN THROUGH THE BIO-0BALLS. BY GRAVITY, AND FLOWS BACK INTO THE POND THROUGHT THE BULKHEADS, WHICH ARE CONNECTED TO THE PVC RETURNS U SEE. POND LOOKS GREAT MIKE. GLAD WE COULD HELP....