Grease Interceptors and How to Maintain Them

Photo shows part of the FOG Pump Out Report
A grease interceptor is a device located between kitchen drain lines and sanitary sewer lines. Grease interceptors capture the fats, oil, and grease flowing down kitchen drains and stop them from flowing to the sewer. To work properly, interceptors must be maintained regularly.
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Types of Grease Interceptors

There are two types of grease interceptors.

  1. Hydromechanical grease interceptors (HGI) (sometimes called grease traps) are installed indoors above or below the floor, or inground outside. Their capacity is measured by the volume of water that flows through the fixture, which ranges from 20-50 gallons per minute.
  2. Gravity grease interceptors (GGI) are installed outdoors and may be aboveground or underground. These devices separate FOG and food waste from wastewater in large tanks that range in size from 1000 to 4000 gallons.

For more detailed information on grease interceptors, view the 2021 State of Oregon Plumbing Specialty Code.

City Inspections

City staff inspect grease interceptors to ensure they are in good working condition and that food service establishments are pumping them out frequently enough to prevent FOG bypass to the City sewer system. The City can issue citations for deficiencies identified with the grease interceptor.

Proper Grease Interceptor Maintenance

An interceptor needs proper maintenance to operate efficiently. A poorly operating or improperly maintained grease interceptor will allow FOG to bypass and enter sewer lines. Not cleaning the interceptor frequently enough can cause private drain line blockages, back-ups, foul odors, and loss of business. Even worse, a FOG obstruction in the City sewer line can cause a sewage overflow to the environment or into other buildings. The City will take enforcement actions against a food service establishment that causes a grease obstruction in the City sewer, and the establishment could also be liable for any damages caused to other impacted homes or  businesses.

Use a Preferred Pumper for Cleaning and Maintenance

Using a pumping company that is part of the Regional Preferred Pumper Program ensures that cleaning and maintenance meet standards established by regional municipalities. Standardized procedures increase the likelihood that grease interceptors are cleaned correctly and keep FOG out of the sewer system. Pumpers registered with the Preferred Pumper Program certify that they will follow pump-out criteria. The City encourages commercial and institutional FOG generators to use a Preferred Pumper.

Clean Grease Interceptors Routinely

Grease interceptors must be cleaned routinely to ensure that grease accumulation does not cause the interceptor to operate poorly and allow FOG to flow to the sewer. The City sets the cleaning frequency of grease interceptors based on the type of establishment, the size of the interceptor, and the volume of flow discharged by the establishment.

Most interceptors need to be cleaned when they become 25 percent full of FOG and solids. However, some high-efficiency HGIs can accumulate up to 75 percent. Routine cleaning will prevent sewer line plugging between the establishment and the sanitary sewer system. If the line plugs, the sewer line may back up into the establishment, and the business will need to hire someone to unplug it.

Report Each Cleaning

A business must file a cleaning report with the City after every interceptor cleaning or pump out. Preferred pumpers can do this on behalf of the business.

To keep your grease removal device working properly, it must be cleaned regularly. This video shows how a grease removal device looks following a proper cleaning and how to report cleanings to the City's fats, oil, and grease inspection program.

Use No Additives

Adding any chemical, enzyme or bacterial substance to break up FOG to any type of grease interceptor violates Portland City Code 17.34Administrative Rule ENB-4.26 prohibits the use of additives, regardless of their composition, because they allow FOG to pass through the grease interceptor and flow directly into the City sewer system. These additives may also damage sewer pipes or interfere with the City’s wastewater treatment operations. Grease interceptors can do the job without additional additives when they are properly sized to manage FOG and receive regular cleaning and maintenance.

Any food service establishment using additives are disqualified under Administrative Rule ENB-4.25 from receiving sewer rate reductions.

Prohibited Additives

  • Chemical Emulsifiers. Cleaners, solvents, caustics, and other chemical emulsifiers do not eliminate FOG. These agents only help move the problem down the line and allow FOG to pass through and build up inside City sewer pipes.
  • Enzymes. Enzymes from animal or synthetic sources temporarily change the physical properties of FOG. FOG treated with enzymes and released to the sewer lines can re-form into solid matter, obstructing sewer pipes and causing sewer backups.
  • Bacteria. Bacteria need a more reliably constant environment than a grease interceptor to thrive due to constant changes in temperature, pH, FOG loading, or water flow. Even if bacteria can survive and flourish, their effectiveness is limited so that FOG can still flow directly to sewer lines.

For any additional questions about FOG, please contact the Environmental Services Cut Through the FOG Program.