Product Description 3P Overflow Siphon Uno The 3P Overflow siphon with skimming inlet, designed to skim surface water, removing debris, oils and other floating contaminants to increase water quality. For installation inside the rainwater tank on the tanks outlet. Attaches with a large backnut, making it suitable for both below ground and above ground tanks. Connection Size DN100 (110mm OD) to fit a 130mm hole in the tank wall.