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Some businesses, commercial facilities, and industries have their septic tank wastes hauled to King County's South Treatment Plant.

South Plant is the only King County-operated facility that accepts waste from septic systems.

King County requires many businesses to get formal authorization before it accepts their waste. King County needs to evaluate whether the waste could harm the treatment plant or the environment.

We know that the industrial waste authorization and application process is complex. Please contact us if you have questions and our staff will be happy to assist you. If you have difficulty viewing or downloading documents, please visit Software Help.

Who needs formal authorization?

Authorization not required Authorization required
(see process below)
Owners of residential septic tanks All other businesses and facilities.

Businesses whose wastewater production is similar to domestic wastewater discharge, such as:

  • Retail shops
  • Daycares
  • Elementary schools
  • Athletic fields
  • Office complexes


Review the Sending Commercial Septage to King County’s South Treatment Plant fact sheet for details, including a list of typical industries that require authorization.

How to get formal authorization

  1. Confirm with your septage hauler that they will be taking your waste to King County’s South Treatment Plant.

  2. Complete a Septage Acceptance Application . As the business that uses the septic tank, you must apply for authorization. Your hauler may not know what business practices created the waste you need hauled.

  3. Submit your form with the required signatures to King County Industrial Waste.

  4. King County will review your forms. The County may ask you to have your septage tanks sampled for pollutants of concern.

    When King County Industrial Waste approves your application, you will be issued an approval letter with an authorization number.

  5. Provide your authorization number to your septage hauler. Your hauler will use the authorization number to complete the King County Hauled Waste Guidelines and Certification Form .

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