The distribution box is the unsung hero of your septic system
A distribution box moves partially treated sewage to the leach field.
The distribution box is the last step before treated sewage is fed into the ground.
Septic tank distribution boxes typically last for between 30 and 40 years.
Distribution boxes don’t need regular pumping but might need occasional maintenance.
Septic tanks are complicated pieces of equipment, often with multiple chambers and separate tanks to handle sewage treatment. If you’ve found yourself wondering “what is a septic tank distribution box?" you’re not alone. In this guide, we’ll explain exactly what it is, how it works, and why it’s so important for the safe treatment and movement of sewage through your septic system.
It’s helpful to know generally how a septic system works before you understand what a distribution box does and why it’s necessary.
Waste enters your septic system. First, waste and wastewater drain through your main sewer line into the trash tank in your septic system. Solid waste and sludge get trapped in this tank, which is the portion of the septic tank you need to check to see if it’s full. Liquid waste eventually spills over into the mixing tank.
The liquid waste is aerated. In aerobic septic systems, an air compressor pumps oxygen into the mixing tank to feed the aerobic bacteria. This speeds up the sewage treatment. In non-aerobic systems, the process happens more slowly and without an input of oxygen.
Solid waste settles out. Many systems have a final settling chamber for the partially treated sewage to sit before heading to the distribution box. Any solid waste should settle out of the sewage and get rerouted back to the previous chamber.
The treated waste is discarded into the soil. Finally, the treated waste seeps into the soil, where aerobic bacteria will continue the treatment process if necessary. The area where the waste is discarded is called the leach field.
It’s worth noting that this is generally how septic systems work. There are differences between the various types of septic systems.
So, what is a septic tank distribution box? It’s a separate underground box that receives the treated sewage from your settling chamber and distributes it to your leach field. It ensures even distribution of the treated sewage so as not to flood a particular portion of your property and to avoid contaminated liquid from seeping into the groundwater too quickly.
Distribution boxes—sometimes called D-boxes—are typically made of one of three materials: concrete, plastic, or fiberglass.
| Concrete | Plastic | Fiberglass |
|---|---|---|
| Will not float | May float to surface | May float to surface |
| High cost | Low cost | Moderate cost |
| ~40-year lifespan | ~30-year lifespan | ~30-year lifespan |
Steel distribution boxes used to be a prevalent option as well, but they’re expensive and can rust, giving them a shorter lifespan of around 20 to 25 years. Most homeowners avoid steel septic tanks and distribution boxes.
There is also a wide variety of styles when it comes to distribution boxes, and the style and interior of the box usually depend on the type of system and leach field you have.
Conventional or chamber system: In a conventional system, the distribution box simply distributes partially treated sewage evenly through the leach field using a series of exit pipes.
Drip distribution system: In a drip distribution system, the distribution box pumps sewage through an exit pipe that eventually enters back into the distribution box. Along the pipe is a series of smaller perforated pipes through which small portions of the sewage can exit as it moves through the exit-and-return pipe.
Aerobic septic system: In an aerobic system, the distribution box is actually a pump tank. The tank can spray the high-quality effluent that comes out of these systems over the lawn for irrigation, or it can pump it into the ground for disposal.
Mound system or sand filter system: These systems also have a pump tank acting as a distribution tank. They pump effluent onto the top of a mound or an area filled with sand and aerobic bacteria for a higher degree of treatment before entering the soil.
Wetland system: These systems use a standard distribution box, but they receive effluent from a wetland area, where additional treatment occurs.
Yes, septic tank distribution boxes are necessary for the safe disposal of treated sewage. There are a few key things the D-box accomplishes.
Evenly distributes effluent to prevent flooding in certain portions of your yard.
Safely distributes effluent according to the type of leach field you have.
Provides additional time for your sewage to receive treatment from aerobic bacteria, which prevents contamination of the groundwater.
In aerobic systems, they can cut down on water consumption and utility bills by providing irrigation.
Finding your septic tank distribution box can be tricky because it and the rest of the septic system components are completely buried. Both your main septic tank and the distribution box or pump tank, though, will have ground access points, so you might be able to locate the cap, which should be level with your lawn.
The exact location will vary based on the type of septic system you have, the location of your leach field, and the layout of your property. In most cases, the access point closest to your home and the main sewer line exiting your structure will lead to your septic tank, and the furthest one from your house—or the closest one to your leach field—will provide access to the distribution box.
Unless you’re adding a chlorine tab to your pump tank distribution box, you shouldn’t access any portion of your septic tank yourself, as the contents of your septic system are hazardous. Instead, call in a local septic tank company to locate, access, and service the distribution box.
Most septic tank distribution boxes will last for around 30 to 40 years, but it depends on the material, location, and other factors. Plastic and fiberglass D-boxes are expected to last for around 30 years, while concrete D-boxes can last 40 or more years.
There are a few things that can shorten the life of your distribution box or require maintenance:
Improper installation can result in immediate damage and issues with effluent distribution.
High groundwater can cause plastic and fiberglass D-boxes to float to the surface. If this happens, you’ll need a professional to reinstall it for you.
Heavy machinery driving over your distribution box can collapse it or damage it, limiting its lifespan.
Soil settlement can lead to uneven effluent distribution, requiring repair or replacement.
Thankfully, septic tank distribution boxes are relatively low-maintenance. Since there isn’t any solid waste in the box as there would be in your primary septic tank, you don’t need to have the distribution box pumped.
Regardless of the type of septic system and distribution box you have, you should have them inspected every three to five years. A good rule of thumb is to have the company pumping your system inspect the main tank and distribution box at the same time. They can identify issues that require maintenance or replacement.
If you have a pump tank acting as a distribution box, you’ll also need to add a chlorine tab every few months to disinfect the water before distribution.
