Saying that your home’s septic system consists of four major components is a bit like saying a car works because it has doors and tires. Beyond the sewage pipe, septic tank, drain field and your soil, a properly functioning septic system has many moving parts with associated terms that may be confusing to you as a homeowner. With that said, having a basic understanding of these terms can be helpful when discussing your home’s septic system with regulators, real estate agents and contractors.
Your Septic System’s Four Major Parts
As noted before, your septic system consists of four major parts.
The sewage pipe carries blackwater, greywater and wastewater from your home and empties it into a septic tank. The septic tank is large enough—usually 1,000 gallons—to handle roughly 40 percent of sewage treatment for your home. When everything is working properly, the septic tank separates sewage into three distinct layers, with liquids running out into your home’sdrain field, which handles the remaining 60 percent of sewage treatment, according to the U.S. Environmental Protection Agency (EPA). Within the drain field the soil, and its marvelous brew of bacteria and microbes, breaks down the liquid safely so your groundwater is not polluted.
Waste Line to Tank
The sewage pipe or waste line, which runs from your home to your septic tank, may on occasion become blocked. Such blockage is relatively easy to clear either from the home or through the cleanout, an access pipe into the system with an aboveground removable cap.
Tank to Drain Field
The septic tank is the first step in household wastewater treatment and, despite seeming to be nothing more than a giant box, has many components. Watertight septic tanks can be concrete, polypropylene or fiberglass, but are always buried. At one end, the waste line from your home attaches to an inlet tee, allowing different types of waste liquid to enter the tank for treatment:
Blackwater - Also known as septage, this is household waste from toilets, urinals and, in some instances, kitchen drains.Greywater - Non-sewage water leaving your home, such as from bathtubs, bathroom sinks and washing machines.Wastewater - A catch-all term for all of the water leaving your home, sewage and otherwise, that enters the septic tank. Effluent - The liquid layer that leaves the septic tank.
A septic tank is septic, or related to bacteria, because it depends on microorganisms to safely break down biologically hazardous human waste.
To safeguard your family, the septic tank has baffles and other safeguards that keep the wastewater flowing outward, rather than backing up, thus minimizing accidental discharge of solids into the drain field:
Baffle - A deflecting device inside the septic tank that prevents floating solids from leaving via the outlet tee; the baffle also controls the flow rate.Gas Baffle - A device inside the septic tank that deflects gas bubbles away from the outlet tee.Outlet Tee - The tee-shaped pipe that allows only effluent to leave the septic tank.
Inside the tank, gravity and bacteria separate the solids (dropping to the tank’s bottom to form sludge), the effluent (the middle and bulkiest layer) and the scum (the materials and gas in effluent that float on its surface).
After allowing natural processes to separate household sewage into scum, effluent and sludge, the effluent empties out into the drain field. The drain field allows the slow seepage of effluent into your property’s soil.
Drain Field into Soil
Many older septic systems drain near ground level into a system of pipes that distribute treated effluent over a large area to soak into the soil. Modern systems may have a mound, in which the drainage pipes carry effluent into distribution lines that empty into built-up layers of aggregate and fill:
Distribution Line - A series of perforated pipes laid in a network to allow effluent to seep into the surrounding soil and aggregate.Drain Field - Also called a leach field, seepage bed or drainage bed, this is the whole area past the septic tank that carries effluent to distribution lines.Mound - Also called a turkey mound or raised system, this artificially created drain field locates distribution lines above the normal grade, with fill added to improve drainage.
Your average backyard soil, teeming with helpful bacteria and microorganisms, breaks down effluent flowing from your drain field. Your septic system’s efficiency can be marred by long stretches of heavy rain (which saturates the soil) or by heavy shade that inhibits evaporation.
Testing Your Septic System
Some specialized vocabulary comes into play when a septic inspector checks a septic system:
Breakout - Septic effluent rises to the surface of your property, rather than percolating down.Hydraulic Load Test - Depending on certain conditions or local ordinances, a Hydraulic Load Test (HLT) may be necessary. This involves adding a specified volume of water to the absorption area (usually via the distribution box) to safely test the system to see if it can properly accept and process the daily flow of water calculated by the septic regulations. For example, if a home has been vacant for more than 7 days a HLT may be necessary to verify proper operation.
By maintaining the major components of your home’s septic system—waste pipe, septic tank, drain field and soil—you preserve your home's value. And, as the EPA says, keeping your septic system healthy not only protects your investment, it safeguards your family's health and the environment.