Septic Systems

Free Septic Sense Workshop
October 19, 2022 from 6 - 8 p.m. (PT)

Sign up for this free online workshop created for Bothell residents and featuring Teri King, the leading septic specialist for Washington Sea Grant.

Co-hosted by City of Bothell and Snohomish Conservation District

Septic - register here button

Septic system basics

Most septic systems are a simple design with a two compartment tank and drain field. The septic tank is a watertight box, usually made of concrete or fiberglass, with an inlet and outlet pipe. The septic tank treats the wastewater by holding it in the tank long enough for solids and liquids to separate. Learn more about how septic systems work.

Sludge and scum

Solids lighter than water (such as fats, oils, and grease) float to the top forming a layer of scum. Solids heavier than water settle at the bottom of the tank forming a layer of sludge. The layers of sludge and scum remain in the septic tank where bacteria found naturally in the wastewater work to break the solids down. The sludge and scum that can't be broken down are retained in the tank until it is pumped. 

Standard drain field 

A standard drain field is a series of trenches or a bed lined with gravel or course sand and buried 1' - 3' below the ground's surface. Perforated pipes or drain tiles run through the trenches to distribute the wastewater. The drain field treats the wastewater by allowing it to slowly trickle from the pipes out into the gravel and down through the soil.

Septic Drainfield

Caring for your septic system

There are many ways to extend the life and functionality of your septic system

Have your septic system inspected

Your septic system needs an annual inspection and needs to be pumped at least every three years, or more frequently depending on what type of system you have. Search for a septic system professional in your area.

Be smart when you hire a septic contractor

Check out the Labor & Industries website to learn how to "hire smart" and protect your home in the process.

Get a copy of your septic system as-built

Health departments often have septic system as-builts stored in a public database. Check your county's health department to see if yours is available.

Looking for other septic-related records? Please submit a public records request.

Septic systems glossary

EPA’s Glossary of Septic System Terminology contains terms commonly used in the wastewater treatment field and their definitions.