Commercial Kitchen Grease Trap Guidelines

Grease traps are required in restaurants and food establishments.

Cooking grease that gets washed off cooking appliances and kitchenware can end up causing significant problems in building drains and BWSC sewers. BWSC’s regulations governing the use of sanitary and combined sewers and storm drains require properly installed and maintained grease traps in all restaurants and food establishments in Boston.

Article III, Section 15, states: “Grease traps shall be required on sewers into which significant amounts of animal or vegetable fat, oil or grease may be discharged so that a discharge concentration does not exceed 100 milligrams per liter.... The Commission shall have the right to inspect such facilities in accordance with Article VII of these regulations.”

The establishment owner is required to keep maintenance records regarding the periodic cleaning of the establishment's grease traps on the Grease Control Log (link below). The log notes the date the trap is cleaned, amount of material removed, and a signature confirming the work was performed. Proper maintenance of grease traps is essential to the smooth and sanitary operation of a food establishment.

Grease Control Log

Two types of grease traps exist:  

• Traps located in an establishment near the fixture it serves
• Large traps located outside the building in the ground that serve the entire kitchen

Significant amounts of grease in buildings and BWSC sewers can come from the following fixtures:

• Pot Sinks
• Rinse Sinks at Dishwashers
  • Note: Garbage disposals should not be installed on these sinks
• Dishwashers Outside Trap Only
  • Note: Dishwashers cannot flow through a point-of-use trap inside a building
• Floor Drains and Sinks
• Automatic Hood Washers

Grease and solids from food establishments are captured in the trap, while water is flushed to the sewer system. Periodically, the trap needs to be opened and the grease and solids removed to allow the trap to continue operating properly.

Note: These methods of cleaning are for guideline purposes only; many traps are designed differently and require specific methods for cleaning. Consult the equipment manufacturer for instructions.

• Grease traps should be cleaned when 25% of the liquid level of the trap is grease or oil, once a month minimum for point-of-use traps, and quarterly for large in-ground grease interceptors
• The cover should be removed carefully to avoid damage to the gasket
• Ladle off the layer of grease and oil floating on top of the water
• Remove any baffles and scrape clean. After cleaning, the baffles can be rinsed off in the sink that flows to the trap
• Using a strainer, scrape the bottom of the trap to remove all non-floatable food particles and debris
• Clean the bypass vent with a flexible probe or wire
• Reinstall baffles and cover
• Record cleaning on Grease Control Log

Note: The grease trap should be completely emptied at least once a month. Many establishments have an independent contractor that specializes in grease trap cleaning perform the work.

All interior grease trap installations are subject to state and local plumbing codes.

Never add bleach, emulsifiers, enzymes, or any other chemical to the grease trap. These agents harm the natural bacteria that eat grease and oils in grease traps. The only additive allowed into the sewer system by BWSC is bacteria. Bacteria consume fat, oil, and grease in the trap, turning them into water and carbon dioxide.

The food establishment’s waste hauler or renderer that removes used fryolator grease and oil normally accepts materials removed from the grease trap. Large in-ground grease traps normally hold 500 gallons or more and are usually cleaned by a contractor
equipped to deal with the large quantities of grease, oil, and non-floatables. It is the responsibility of the establishment owner to ensure the trap is completely cleaned.

For additional information regarding the proper maintenance and care of grease traps, please contact Enforcement at 617-989-7299.

Grease Trap Brochure