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Businesses that use Septic tanks

Information about King County Industrial Waste authorization for businesses that use septic tanks.

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

Sources that generate domestic septage and non-domestic septage shall use a hauler approved by King County for the collection, transport, and discharge of their waste into the King County POTW.

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

Learn more with the Sending Commercial Septage to King County's South Treatment Plant Fact Sheet (1.44MB)

Two septage hauling trucks parked on a concrete strip. A pipe is connected from the tank of one of the trucks into a hole in the concrete.
The South Plant septage disposal facility allows four trucks to dispose of septage simultaneously.

Who needs formal authorization prior to having their waste hauled?

Businesses and facilities must obtain written authorization from the King County Industrial Waste Program (KCIW) prior to having their waste hauled for discharge into the King County POTW.

Authorization not required Authorization required
Owners of residential septic tanks  All other businesses and facilities that use septic tanks

Businesses with similar wastewater production as domestic wastewater discharge:

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

How to get formal authorization

  • Confirm your waste will go to King County's South Treatment Plant

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

  • 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.

    Download the Septage Acceptance Application (32KB)

  • Submit your form to King County Industrial Waste

    Print and sign the application. Scan the signed documents and email it to the King County Industrial Waste program at

  • King County Industrial Waste will review your forms

    Upon review, 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.

  • 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 (59KB).

Find a hauler or pumper

Public Health - Seattle & King County

Licensed septic professionals in King County

Washington On-Site Sewage Association (WOSSA)

Member companies listed by county