This filter automatically cleans itself, all with the simple twist of a knob! When in the 'run' position the water undergoes a 4-stage purification process. Simply turn the knob to "Clean" and the foams are then squeezed by up to 1,000lb of water pressure, forcing out pond sludge. The back-flushed dirty water is then pushed out through the second waste outlet (typically down the drain or flowerbeds). The filter  boasts a built-in UVC and guarantees clear water for ponds up to 30,000 litres. (Figures based on pond in full shade with waterplants - 5,000 litres for ponds in full sun).