Built-in overflow for lateral glass boreholes, ø43 to 45 mm (1.7 to 1.8 in.), on the rear or lateral wall of the aquarium, with surface and bottom suction up to about 1,500 l/h (400 US gal./h). Water outlet ø40 mm (1.6 in.). For easy installation and quiet operation, we recommend the use of overflow hose set