A built in overflow is the most efficient method of draining aquarium water to a filter. If your aquarium does not have built-in overflow, Your Choice Aquatics OF series overflow box are the best means for getting water from an aquarium to a filter system without expensive modifications to the tank. High quality and economical hang-on overflow box allows you to easily add a sump, refugium or wet/dry filter to your system. U-tube design allows for easy and convenient installation. Adjustable pre-filter height allows you to adjust the water level inside your aquarium. Self priming after initial setup, in the event of a power failure. Nano up to 30 Gal 4"x2.5"x8" 4"x1.5"x6" 200GPH 3/4" x 1 pipe; OF-300 up to 60 Gal 6"x3"x10" 6"x2.5"x6" 300GPH 1 x 1 pipe"; OF-800 up to 120 Gal 8"x3"x10" 8"x2.5"x6" 800GPH 1" x 1 pipe; OF-1000 up to 150 Gal 9"x3"x10" 9"x2.5"x6" 900GPH 2 x 1" ( 2 pipes ); OF-1200 up to 200 Gal 10"x3"x10" 10"x2.5"x6" 1000GPH 2 x 1" ( 2 pipes ); OF-1800 up to 320 Gal 12"x4"x10" 12"x2.5"x6" 1600GPH 1-1/2" 1 pipe