Septic systems are installed in about 1 in 4 homes in the U.S., and they are especially prevalent in rural areas that are not served by municipal sewer service. Rather than pumping waste through sewer mains to a central sewage treatment facility, a septic system pumps solid and liquid waste from the house out into a drain field and underground septic tank.
How Septic System Works
In a traditional septic system, all water and wastes carried by that water flows down the home's drain system and through one main sewer pipe to the septic tank. The flow of wastewater may be a matter of simple gravity, or it may be enhanced with an electric pump. The septic tank holds the waste material long enough for the solids to settle to the bottom as oil, grease, and liquids — the scum later — float to the top. When the tank reaches capacity, the liquids lying on top of the scum later flow onward into a series of porous pipes to a drain field prepared with gravel and other aggregates that helps disperse the liquid waste. The liquids slowly filter down through the soil as bacterial action breaks down the pathogens. By the time the liquid waste filters down to groundwater supplies, it is virtually sterile.
Meanwhile, the solids in the tank break down under the affect of anaerobic bacteria, creating a sludgy material that collects in the bottom of the tank. If the bacterial action is effective, these solid wastes are greatly reduced in volume as they break down.
Anatomy of a Septic Tank
The septic tank water-tight container made of concrete, fiberglass, or polyethylene buried in the ground in an area near the house. It includes an inlet pipe where all waste from the home's sewer pipe enters the tank and an outlet pipe that allows liquids to flow onward to the drain field. The top of the tank is buried slightly under the surface of the soil, invisible except for one or two inspection tubes and a manhole cover that is used to pump the sludge from the tank when it becomes necessary.
When to Have Your Septic Tank Pumped
The EPA recommends that a septic tank should be inspected every two to three years, with mechanical pumping typically required every three to five years to empty the tank. Systems that are undersized or that see very heavy use may require pumping annually. Some systems have electrical float switches, pumps, or mechanical components, and these need to be inspected more often, typically once each year.
Pumping is the process of removing sludge from the bottom of the septic tank, and this needs to be done before the sludge builds up to a level where it blocks the outlet pipe through which liquids flow into the drain field. The frequency with which this needs to be done depends on several factors:
- Size of household: Larger households, predictably, generate more waste, and thus fill up the septic tank faster.
- How much wastewater is generated: The sheer volume of wastewater flowing into the septic tank can affect how fast the septic tank fills up.
- The volume of solids in the wastewater: Households with many toilets, or who make frequent use of garbage disposals, tend to fill up the septic tank quicker.
- Septic tank size: Larger tanks can hold more solid sludge, and thus will need less frequent pumping.
There are ways to help estimate about when you should have your tank pumped. As an example: an average four-bedroom house may have a 1,200 to 1,500 gallon tank and with a family of four, you should expect to have the tank pumped every 3 to 5 years with typical use.
How a Septic Tank Is Pumped
If you have a septic service professional who inspects your septic tank regularly, they will tell you when it is time to pump out the sludge from the tank. Generally, this is when the floating scum layer that lies between the sludge and the floating water is within about 6 inches of the outlet pipe leading to the drain field.
The septic service arrives with a large tanker truck with vacuum equipment, and technicians insert a large hose into the septic tank through the manhole after the cover is removed. As the truck's equipment sucks out the contents of the septic tank, a technician usually stirs the contents of the tank with a muckrake to break up the solids and mix them with the liquid material to make pumping more efficient. Costs for pumping a septic tank range from $200 to $500 depending on the region in which you live and the size of the septic tank.
Tips for Maintaining Septic System
There are several proactive measures you can take to ensure that your septic system operates efficiently and to reduce the frequency with which pumping is necessary:
- Reduce water usage. Using high-efficiency, water-saving plumbing toilets and faucets can greatly decrease the amount of water that goes into the septic system. Repairing leaks and drips is another way to reduce the overuse of water that can cause the septic tank to fill faster.
- Reduce solid wastes: Monitoring the solid waste that enters the septic system is another way to keep it working properly. Trash that is either washed or flushed down the drain can overburden the septic system. Don't flush anything other than toilet paper down the toilet, and avoid using a garbage disposer that puts organic food wastes into the septic system. Throwing things in the trash takes only a little effort, but it will make a big difference in the management of the septic system.
- Direct rainwater away from the drain field. Downspouts and landscape grading that funnel water onto the septic system's drain field can interfere with its ability to disperse water from the septic system.
- Don't drain hot tubs into the drain system. This can put undue stress on the septic system; instead, drain water from hot tubs or swimming pools into the yard, away from the drain field.
- Avoid putting chemicals down the drain. Chemicals can interfere with the bacterial action that breaks down solid wastes, so avoid flushing them down the drain. This also includes various commercial septic tank additives, which generally do more harm than good. Unless a trusted professional has prescribed such an additive, don't use any septic tank chemicals.
US EPA, OW. “How to Care for Your Septic System.” Overviews and Factsheets, June 16, 2015. https://www.epa.gov/septic/how-care-your-septic-system.
US EPA, OW. “How Your Septic System Works.” Overviews and Factsheets, June 16, 2015. https://www.epa.gov/septic/how-your-septic-system-works.