Input Pipe: This pipe carries effluent from the septic tank into the distribution box. A distribution box is a concrete or plastic structure that plays a pivotal role in the septic system. Without it, wastewater would flood one section of the drain field while starving others, causing premature system failure. Whether in a home or an industrial facility, this box keeps your electrical setup organized, functional, and efficient. Distribution boxes also provide a readily accessible means of locating the leaching device, making flow adju e typically made of reinforced concrete with plumbing “knock outs” into th box. Twist and lock 4” pipe seals and plugs are easily installed and fit all 4” plastic pipes.