What Is a Septic Distribution Box?

A distribution box (often called a D-box) is a small watertight box between the septic tank and the drain field. Effluent from the tank flows into it, and each drain field line leaves it through its own outlet.

Explanation

Florida's septic rule describes a standard drain field as "a distribution box or header pipe" plus a drain trench or absorption bed (Rule 62-6.002(55)). So not every system has a D-box: some use a header pipe instead.

Where a distribution box is used, Rule 62-6.014(1), F.A.C., sets these standards:

• It must be watertight, durable, strong enough, and big enough for the number of drain field lines.
• Each drain field line must connect to the box on its own.
• The inlet sits at least 1 inch higher than the outlets, and all outlets must be level with each other.
• The box must be a separate unit from the septic tank and set level on solid ground or in gravel (mineral aggregate).

Level outlets matter because they let each line take its share. The EPA lists checking the distribution box "to make sure drain lines are receiving equal flow" as part of a septic inspection.

Florida's rule does not count minor structural corrections to a distribution box as a repair (Rule 62-6.002(51)), so a small fix may not need a repair permit. Replacing a failed box or drain lines is a repair, which usually needs a permit. Where roots clog a distribution box or drain line, Rule 62-6.015(6)(e) treats removing the roots and replacing damaged drain field material as meeting the repair permit, once the work is inspected, if that restores the system. Ask your permit office if you are not sure whether your job needs a permit. Published ranges put distribution box work at about $500–$1,500.

When to seek help

• Standing water, damp spots or sewage odors over the drain field.
• Tree roots grow near the tank or drain lines.
• Your inspection report says the box is broken, tilted or holding water.

Learn more in how a septic system works in Florida and septic repair and drain field costs. Check what a repair needs in Florida septic regulations, or compare septic repair companies and septic inspection companies.

Related terms

• Drain field (leach field)
• Effluent filter
• Baffle
• Mound system