When buying a home in Snohomish County its common to encounter homes on a private or shared septic system. For those that may not know, a septic system in an on-site- sewer system for residential homes.
Why would home builder choose to use a septic system over city sewer? In most cases there isn't city sewer available when a home is built in the more rural areas.
What cities will I encounter a septic system in?
In other county cities may have septic systems but they're not nearly as common place. Here is a 13 minute video on septic systems, how the basics work, and the residential septic addendum used in a property purchase or sale in Snohomish County.