Septic system drawing An Introduction to Septic Systems - the Basics

  • SEPTIC SYSTEM BASICS - What is a septic system? - the basics for home owners and buyers of a home with a septic tank and drainfield or alternative septic system design
  • POST a QUESTION or READ FAQs about home septic systems: what is a septic tank, what is a drainfield? How do septic tanks work? How do drainfields work? What are the recomended steps to clean out or maintain septic tanks and drainfields?

What is a septic system?

This article explains what a septic system is, with a brief description of how septic systems work and what are the main components of a septic tank and drainfield system. This article describes the basic function, design & care of private septic tanks & drainfields or soakaway beds.

Key articles for people unfamiliar with septic systems are listed here:

Green links show where you are. © Copyright 2015, All Rights Reserved.

An Introduction to Septic Systems - How do Septic Systems Work?

If you don't know if your building is connected to a public sewer or a private septic system, see SEPTIC or SEWER CONNECTION?.

Readers should also See Septic Guide for Home Buyers or Owners and Septic Maintenance Repair. Other helpful but still basic articles for owners of a property with a septic system include:

What is a Septic System? Or What's a Septic Tank? What's a Drainfield? How do they work?

Sketch of a conventional septic system showing tank and drainfields

A "septic system," also referred to as a private, on-site waste disposal system, receives waste water and solids from a building's plumbing facilities (bathrooms, kitchens, shower, laundry), treats, and then disposes of the effluent from this waste, by permitting it to absorb into soils at the property.

Wastewater or septic effluent treatment is accomplished by bacterial (and other microorganism) action in the "septic" or "treatment" tank and it is mostly accomplished by bacteria in the soil around and below the effluent absorption system, or "drain field."

This bacterial action is needed to reduce the level of pathogens in the effluent discharges from the waste system into the soil. In addition to reducing the level of pathogens and the reduction of organic waste to a combination of new cell masses, CO2, and water, wastewater treatment removes organic matter, nitrites and nitrates, and phosphorous. In an absorption field the soil performs an additional role of filtering the septic effluent.

Where are the Septic Tank & Leachfield Usually Located on a Property & How are these components Laid-Out ?

The septic tank is usually located close to the building, perhaps just ten feet away, but on difficult sites a grinder pump may instead send wastewater to a more remote septic tank and drainfield. Incidentally, depending on where you live, the "drainfield" that absorbs & treats the final septic wastewater or effluent might be called a leachfield, leaching bed, drainage trench, soakaway bed or other terms. (Contact Us to suggest other septic system terms to include here.)

Septic system drawing

The principal components of a private on-site waste disposal system usually include the following:

Below is a simple sketch of a septic tank showing how solid waste leaving the building thorugh its main drain or wastewater piping or "sewer line" or "septic line" is retained inside the tank while liquid effluent flows to the drainfield. (Click images to see an enlarged version). Here are the main components of a septic system and a brief description of what each does:

Septic tank sketch
  • Wastewater Piping connecting the building to the treatment tank conducts wastewater from toilets, sinks, tubs, showers, out to a septic tank. Wastewater from toilets is called "black water" and wastewater from sinks is called "graywater"
  • A septic tank or sewage treatment tank which retains solid waste, letting liquid waste flow to an onsite disposal system.

    Be sure to see SEPTIC TANK PUMPING SCHEDULE since pumping the septic tank regularly is the single most useful thing you can do to extend the life of a septic system.
  • Effluent piping connecting and conducting clarified effluent from the treatment tank to a distribution box
  • A distribution box connecting the effluent line from the tank to the absorption system or "drain field" - SEPTIC D-BOX INSTALL REPAIR
  • An absorption system which permits effluent to drain to soils below and some of it to evaporate to air above. There are many ways to get rid of septic effluent, described at SEPTIC SYSTEM DESIGN BASICS and at SEPTIC SYSTEM DESIGN ALTERNATIVES, or see the list and definitions given at Master List of Septic System Types
  • A bio-mat or bio-mass of pathogen-digesting bacteria which forms in soil below the absorption system. The bio-mat is what makes the wastewater sufficiently sanitary to discharge into the ground.

Many variations on this general scheme are used, depending on local climate, soil conditions, available space, economy, and available materials. Special equipment and systems may be designed for problem or difficult sites such as rocky or wet ground, permafrost, or wet tropical marshlands.


Continue reading at SEPTIC INFO for HOMEOWNERS, BUYERS or select a topic from the More Reading links or topic ARTICLE INDEX shown below.


Suggested citation for this web page

SEPTIC SYSTEM BASICS at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

More Reading

Green link shows where you are in this article series.


Frequently Asked Questions (FAQs)

Click to Show or Hide FAQs

Ask a Question or Search InspectApedia

Use the "Click to Show or Hide FAQs" link just above to see recently-posted questions, comments, replies, try the search box just below, or if you prefer, post a question or comment in the Comments box below and we will respond promptly.

Search the InspectApedia website

Technical Reviewers & References

Publisher's Google+ Page by Daniel Friedman

Click to Show or Hide Citations & References