The five causes are: a settled or tilted box, outlet clogs from solids carryover, root intrusion or crushed laterals, cracked or deteriorated box structure, and a saturated drainfield that mimics D-box symptoms. A septic distribution box (D-box) is a concrete or plastic junction that evenly distributes wastewater from your septic tank to all drainfield lateral lines. When it fails, symptoms include uneven wet spots in the yard, slow indoor drains, and sewage odors. Regular inspection and. In this guide, I have discussed ten of the common problems with a septic tank distribution box (D-box) and how to fix them. Clogging If you've had your septic system for a while, you have probably run into clogs from time to time. The D-box then channels the effluent. The distribution box is the unsung component that keeps your drain field working evenly.