Septic tank maintenance

When functioning properly, an Onsite Sewage System (OSS) will treat and dispose of effluent safely. Because these systems are outside our homes and underground, problems can be easily missed and lead to public health concerns. Some OSS problems start small and can become more involved and expensive if not repaired in a timely manner. Therefore, regular monitoring and maintenance of these systems are important, not just to public health, but your wallet and overall functionality of your home.


According to local and state regulations, all septic systems require regular operation and maintenance. Due to the number of different systems available and complexity of each system, the frequency and type of maintenance depends on your system type. If you are unsure which type of septic system you have, you can look up your records on the Mason County Land Records Search. Once you know your system type, you can use the table below to find your inspection/maintenance frequency and who can perform the inspection/maintenance to meet requirements.

Septic maintenance schedule

Mason County maintenance database and monitoring program

Per WAC246-272A-0015, Mason County is required to inventory all OSS and track all OSS maintenance reports. Therefore, all Onsite Sewage System Professionals are required to submit all maintenance reports to Mason County within 30 days of an Inspection and/or Pumping. Providers upload their reports onto an online database hosted by OnlineRME. Aside from making sure owners are operating and maintaining their OSS, this system is used for permit reviews, home sales, and anything else that may require a snapshot of a septic system maintenance history.

As funding allows, Mason County staff will monitor this database of reports and respond to reports that could result in public health concerns or violations.

Possible Letters owners may receive as part of this program:

  • Unsatisfactory Event Letter: This initial letter is an attempt to make sure the owner is aware of a reported problem with their onsite sewage system and obtain a timeline for corrective actions. An example of this could be a broken septic tank baffle or failing Drainfield.
  • Lack of Annual Operation and Maintenance Letter. Certain types of OSS were permitted and approved with an annual operation and maintenance requirement (ex. ATU, Glendons, Other proprietary products, and more). These systems are tracked in the database to ensure these requirements are being met. This letter is to remind the current owner of these requirements and provide notification when out of compliance.

Learn more about operating and maintaining your on-site sewage system