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How do Septic Systems Work?

Septic systems can be very confusing to many prospective homebuyers, especially if you currently live in an area served by city sewer. Septic systems and municipal sewer systems are similar that they both dispose of and treat wastewater. 

One main difference is with a septic system is that homeowners need to coordinate periodic maintenance to keep it operating properly. Just as you would change the oil in your car or scoop the ashes out of your fireplace, homeowners must maintain their septic system to keep it functioning properly and to extend the system’s life. So what are some of the basics of a septic system?

What is the difference between a Holding tank and a Septic tank? 

 A holding tank does not allow any of its contents to leach away into the ground, whereas a septic tank will allow waste water to run through a drainfield (also called a leaching field) where bacteria breakdown of some of its solid contents, providing the final treatment of the wastewater. Holding tanks require frequent pumping depending on the water use in the home. Once the holding tank fills up, an alarm will notify the homeowner that it is full and requires pumping. 

What is a septic system and how does it work? 

A septic system is used to treat liquid wastes to prevent contamination of drinking water wells, groundwater, and nearby lakes and streams. A septic system typically consists of:

  • a septic tank, which is a watertight, buried tank made of concrete, fiberglass or polyethylene;
  • an inlet pipe and an outlet pipe; 
  • baffles to prevent solids from leaving the tank, and
  • a drainfield, typically consisting of perforated pipe laid in washed rock.

All drains in the home converge to a single pipe, and the waste that comes from the drains in your home (from faucets, showers, washing machine and toilets) pass from the drain line into your septic or holding tank that is buried outside. The septic system holds the wastewater long enough to allow the heaviest particulate matter in the waste, called sludge, to sink to the bottom of the tank. The fats, oils, and proteins float to the top of the tank to form a floating scum layer. The tank retains the solids until they break down (with the help of good bacteria in the system), and the treated wastewater (effluent) then flows into the soils of your property through the drain field. Compartments and baffles in the septic tank prevent the sludge and scum from leaving the tank and traveling into the drainfield area. 

Newer tanks have risers with lids at or above the ground surface to allow easy location, inspection, and pumping of the tank. Minnesota Code recommends pumping your septic tank at least every 3 years to remove the solids from the tank which is one of the leading causes of premature failure. Most septic tank pumpers will also inspect the other components of the system at that time and will let you know if there are any concerns about the system.  

If properly designed, installed, and maintained, your septic system can provide excellent treatment of wastewater for many years.