All About Septic Systems

What Is a Septic System?
Sometimes referred to as “on-site sewage systems,” septic systems are underground wastewater treatment structures that use a combination of nature and time-tested technology to treat wastewater from household plumbing produced by bathrooms, kitchen drains, and laundry.

How Does A Septic System Work?
A typical septic system consists of a septic tank and a drainfield. All water runs out of your house from one main drainage pipe into a septic tank — a buried, water-tight container usually made of concrete, fiberglass, or polyethylene. Its job is to hold the wastewater long enough to allow solids to settle down to the bottom (forming sludge), while the oil and grease floats to the top (as scum). Compartments in the tank and a T-shaped outlet prevent the sludge and scum from leaving the tank and traveling into the drainfield area.

The liquid wastewater (effluent) then exits the tank into the drainfield. If the drainfield is overloaded with too much liquid, it will flood, causing sewage to flow to the ground surface or create backups in toilets and sinks.

Finally, the wastewater percolates into the soil, naturally removing harmful coliform bacteria, viruses, and nutrients.

Septic system illustration
For proper maintenance of your septic system:

  • Regularly inspect your system, and pump your tank as necessary.
  • Use water efficiently.
  • Don’t dispose of household hazardous wastes in sinks or toilets.
  • Plant only grass over and near your septic system. Roots from nearby trees or shrubs might clog and damage the drainfield.
  • Don’t drive or park vehicles on any part of your septic system. Doing so can compact the soil in your drainfield or damage the pipes, tank, or other septic system components.


For more information on your specific type of septic system, click a link below:

The above generally describes a gravity system, the most common and straightforward OSS. However, where soil conditions or terrain are not optimal, other types of OSS are installed.

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Illustration courtesy WSU Beachwatchers