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On-site sewage/septic system inspections

Learn about septic system inspections and their benefits.

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On-site sewage/septic system owner requirements

As an owner, you need to have your sewage/septic system inspected and maintained regularly. This may include repairs and replacements as your sewage/septic system ages. If these systems are not maintained, they can have harmful impacts on groundwater and pollute lakes, streams, and beaches. They can even cause sewage to surface in your yard or back up into your house. To prevent this, a septic system owner also needs to operate their system properly. For example, throw all food waste into the compost or trash can instead of tossing it down the drain.

The State code gives these requirements for how often a septic system must be inspected:

  • Conventional gravity systems need to be inspected every 3 years.
  • Pressure distribution, mound, and sand filter systems need to be inspected every year.
  • All other types of septic systems like ATUs and drip irrigation systems need to be inspected every 6 months (unless the manufacturer specifies, they should be inspected more frequently).
  • All septic systems that serve a food service establishment must be inspected at least once every year.


How an inspection benefits you

Prevents pollution and illnesses

Keeping your system in good operating condition prevents sewage from entering: drinking water sources, creeks, rivers, and bays used for recreation and shellfish harvest.

Saves money

During an inspection, a maintainer can find small problems with your septic system that are easy and cheap to fix. These fixes may help you to avoid larger expensive fixes in the future.

This is also a cost-effective way to protect the life of your septic system, because repairing or replacing a failing system can be very expensive.

Reduces the risk of failure

Early identification of smaller problems can prevent large-scale system failures. A failing septic system may result in a sewage back-up inside your home. It could also expose your family, pets, and nearby waters to leaked raw sewage containing harmful pathogens. This exposure could put families and neighbors at risk.

Identifies need for pumping

Rather than regularly scheduled septic tank pumping, have your tank inspected and only pumped when needed. Different size septic tanks, the use of a garbage disposal, and other factors may increase or decrease how often your tank needs pumping. An inspection costs less than pumping the septic tanks, so if you only have the tank pumped when it needs to be pumped, you can save money.

Learn more about pumping your septic tank.

When to hire an On-site System Maintainer to perform an inspection

Your maintenance schedule depends on what kind of system you have, and other factors related to your property.

When hiring a King County certified Pumper or On-site System Maintainer (OSM), you should:

What happens during an inspection?

The On-site System Maintainer will inspect your system components:

  • Septic and pump tanks
  • Treatment component (if applicable)
  • Distribution system
  • Drainfield and the reserve areas

Then, they will submit a report to Public Health - Seattle & King County about the status of your system. Smaller problems can be fixed during the inspection. If a larger fix is needed, the maintainer will work with you to identify the best solution.

Download a sample Operation/ Performance Monitoring Report form (130 KB)

  • Official copy of this form is made available only to licensed OSM.