Reef Octopus RX40 black tube overflow box is designed to make it easy to set up an aquariums’ water flow system to and from the aquarium. The translucent smoked black acrylic tube hides all the necessary pluming. Because we utilize a unique overflow and return design in our aquariums, the Black Tube Water Flow system is specifically designed to best support and work with the Reef Octopus Luxury aquariums setup. This system uses a unique bulkhead with two openings for the drain and return plumbing through one bulkhead. It also contains 2 useful 1/4″ JG ( John Guest) pipe ports for adding the effluent of a calcium reactor, kalk feed or top off water.