A D-Box is a small tank that has one inlet and multiple outlets that uniformly disperse the flow of the effluent to several lines of a disposal field. A D-Box is very useful when inspecting a failing disposal field to determine possible problems within the system. With expert engineering and solutions in concrete, fiberglass, and metal, we help you build smarter, faster, and stronger. Jensen Precast Is Now Jensen Infrastructure. With its AASHTO HS20 load rating, Christy enclosures are optimized for use on roadways that experience heavy vehicular traffic. The wastewater plumbing distribution box, or D-box, is a key component of any sewage disposal system. Water effluent (wastewater) drains from the septic tank and enters the distribution box. Have any questions? Need a. Jefferson Concrete Corp.