How Does a Septic System Work?

When you rinse your hair in the shower, wash off a dinner plate in the kitchen sink, or flush a toilet, you may not give much thought to where all that wastewater goes. But if you live on a property with a septic system, it’s actually important for you to understand the inner workings of this essential wastewater management system. From the pipes in your home to the drain field in your backyard, here’s how a septic system works.

Parts of a Septic System

To better understand how a septic system works, it’s helpful to know the different parts of the septic system and how they all connect to carry wastewater away from your home, ultimately returning it as treated water into the soil.

Exit Pipe

The exit pipe is where the wastewater, which comes through your home’s plumbing from drains in appliances, sinks, toilets, and bathtubs, will move out of the home and toward the septic system.

Baffles

The baffles are the inlet and outlet pipes to the septic tank. Wastewater travels from the exit pipe of the home to the inlet baffle of the septic tank. When the water is partially treated, it’s ready to later move to the outlet baffle at the other end of the septic tank.

Septic Tank

The septic tank is a large, buried container made from plastic, fiberglass, or concrete. This tank is designed to hold wastewater, including black water from toilets and greywater from sinks, showers, and appliances.

Effluent Filter

The effluent filter is located near the outlet baffle of the septic tank. This filter helps remove contaminants like oils, fats, and grease from wastewater before it continues through the septic system.

Distribution Box

The distribution box, or D-box, connects to various pipes through a drain field, where wastewater goes for final treatment and slowly disperses into the ground. The distribution box helps evenly distribute wastewater to different pipes for proper treatment and dispersal without overwhelming one pipe.

Drain Field

The drain field is where the partially treated wastewater, or effluent, from the septic tank flows for final dispersal into the soil. The field is made up of several leach lines or septic lateral lines.

Leach Lines

Leach lines are positioned along the length of the drain field. They have perforations to let effluent drain slowly into the soil, where bacteria help finish treating the wastewater before it returns back to the groundwater and local ecosystem.

How a Septic System Works

So, how does a septic system work, anyway? There are several steps to the process, and it all starts with water inside your home.

1. Water Moves From Indoors to Outside

First, any wastewater from around the home—such as from toilets, sink drains, tubs, showers, or appliances—will drain away into the pipes of the home and through to the sewer line of the home. This wastewater then travels to the exit pipe to take it out of the home and toward the septic system.

2. Wastewater Is Treated in a Septic Tank

Next, the wastewater travels into the inlet baffle and goes into the septic tank. In this tank, the solids in the wastewater separate and sink to the bottom of the tank while the water sits just above it. Any remaining liquid contaminants, like oil or grease, float to the top. These floating contaminants are known as scum, and the solids that sink to the bottom of the tank are known as sludge. Bacteria that live in the tank help break down some of the waste.

The water continues flowing down the line while the sludge and scum remain in the tank, and the water is treated at an effluent filter before exiting the septic tank as treated water through the outlet baffle.

3. Effluent Moves to the Drain Field

Finally, the effluent travels to one or more distribution boxes and to the septic lateral lines. The effluent slowly disperses out into the soil, where it is further treated by aerobic bacteria. The water eventually reaches the groundwater after being fully treated by the bacteria.

Alternative Methods

There are other types of septic systems than this conventional setup, though, and they work in slightly different ways. For example, aerobic treatment units add oxygen to the septic tank to feed aerobic bacteria, an ideal setup for properties with soil that isn’t well-suited to treating effluent. Another example is recirculating sand filter septic systems, which use pumps to move wastewater to sand filters for treatment.

Septic System Maintenance

Maintaining your septic system is important to prevent clogs and leaks that can cause expensive damage to your septic system and home’s plumbing. Here are some ways you can maintain your septic system:

• Pump the septic tank: Pump the septic tank often, about every three to five years, to remove sludge buildup.

• Schedule inspections: Hire a pro to perform annual inspections to catch any minor repairs before they become bigger problems.

• Replace the biomat: The biomat is a layer of bacteria and other biomaterials under the soil in the drain field. Over time, it can build up and cause clogs. Pumping the tank helps prevent biomat problems, but older systems over 25 years may need biomat replacement.

• Avoid flushing or draining certain items: Too many fats and oils, food waste, sanitary items, and even certain chemicals and skin care products can clog the septic tank.

Septic System Life Span

The life span of a septic system is 20 to 40 years, depending on factors like what material the septic tank is made of and how often you schedule professional sludge pumping. Concrete septic tanks tend to last the longest, up to 100 years, while plastic has a shorter life span. By hiring a local septic tank company to pump the tank every three to five years and perform annual inspections, you’ll get more life out of the septic system.

Septic System Costs

Whether you need to install a new septic system entirely or you’re just budgeting for the next inspection, there are several costs to consider when it comes to owning a septic system. Some costs you can expect for septic systems may include:

• Septic system installation cost: $3,500–$11,750

• Septic system inspection cost: $200–$900

• Septic tank pumping cost: $250–$1,250

• Septic system repair cost: $630–$3,000