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Frequently Asked Questions (FAQ) About Grease

For Seattle Restaurants and Food Service Establishments

What is a grease trap or grease interceptor and how does it work?

Grease traps and interceptors are devices designed to keep fats, oils and grease (F.O.G.) from entering your sewer line and the public sewer line. They can be located inside or outside of your kitchen. In general, they are designed to retain wastewater long enough for grease in the water to cool, solidify and separate from the remaining wastewater. Once the grease separates, it can be disposed of properly.

FOG grease trap

Do I need to have a grease trap or interceptor at my restaurant or food service establishment?

Any establishment that handles any type of food should install a grease trap or interceptor. Even small food service providers like coffee shops who serve products with dairy should install a grease trap or interceptor to keep F.O.G. from going down the drain. An establishment will be required to install a grease trap or interceptor if a side sewer has a visually evident accumulation of fat, oil or grease. Refer to the 2009 Uniform Plumbing Code (available at your public library) for sizing criteria.

How much does a grease trap or interceptor cost and who do I call to get one installed?

Grease traps vary in cost, but generally start at $3,000. This price does not include the cost of plumbing or installing. Please refer to the F.O.G. Service Providers list (pdf) for contractors who can provide more information.

Who determines if I need a grease trap or interceptor?

If your food service establishment handles food and washes dishes, you most likely need to install a grease trap or interceptor. Seattle Public Utilities (SPU) may require an established restaurant to install a device if it is determined that the restaurant is discharging grease into the sewer system. Public Health will require the installation of a grease trap or interceptor for all new or remodeled restaurants that apply for a plumbing permit.

Who is responsible for installing a grease interceptor?

Every establishment that handles food of any sort - from a coffee shop serving milk and other dairy products to a restaurant preparing deep-fried foods - is most likely discharging F.O.G. All food service providers are responsible for installing a device to keep F.O.G. from entering your side sewer and the public sewer line.

What if I don’t install a grease trap or interceptor?

If your establishment handles any food that contains fat, oil and grease, you might eventually encounter a maintenance problem such as a blockage in the side sewer line. A blockage can create a sewer backup situation and ultimately a potential health problem for the establishment. If the problem is in the side sewer line, then the establishment is directly responsible for paying for the cleanup costs and property damage. An establishment is also required by Seattle King County Public Health to close for business until an inspector certifies all health issues are resolved.

If the blockage is in the public sewer main and SPU can verify that the practices of a specific establishment has caused the blockage, then that establishment may have to pay for the public cleanup costs, property damage and public sewer maintenance costs to relieve the blockage. The establishment may also be required to install a grease trap or interceptor or upgrade an existing device to intercept food and F.O.G.

How often should I clean my grease trap/grease interceptor?

A grease trap or interceptor should be regularly maintained to meet the 25% Rule – no more than 25%, by volume, of the trap or interceptor should accumulate of food and F.O.G. If more than 25% of food and F.O.G. accumulate in the trap or interceptor, it is more likely to not be working properly and discharging food and F.O.G. into your side sewer and the public sewer system. Exceptions to the 25% Rule are for devices that are designed to retain more than 25% F.O.G. and will be specifically stated in the manufactures specification.

Each establishment should work out a specific cleaning schedule that is right for their business. Some establishments will need to clean their trap or interceptor more often than others. It is important to remember that implementing kitchen best management practices, such as scraping your plates, pots, and pans, will reduce the amount of food and F.O.G that discharge into a trap or interceptor, therefore will decrease the frequency of cleaning.

How do I clean and maintain my grease trap/grease interceptor?

Grease trap or interceptor maintenance is usually performed by permitted haulers or recyclers (See F.O.G. Service Providers list (pdf) for contractors who do this type of work). If you choose to have your staff clean your grease trap, see detailed instructions below for a basic grease trap:

FOG grease trap diagram

  1. Dip the accumulated grease out of the trap and deposit in a watertight container.
  2. If possible, remove the baffles which are devices used to regulate the flow of liquid through the system.
  3. Scrape the sides, the lid and the baffles with a putty knife to remove as much of the grease as possible, and deposit the grease into a watertight container.
  4. Remove solids from the bottom with a strainer or similar device.
  5. Replace the baffles and the lid.
  6. Record the date, name of grease hauler or recycler (if used), or employee conducting work, and volume of grease removed on the maintenance log (pdf).
  7. Contact a hauler or recycler for interceptor waste disposal. F.O.G. Service Providers list (pdf). And remember to keep this waste separate from your used fryer waste grease. Contractors who pick up and dispose used fryer grease are listed on the F.O.G. Service Providers list (pdf).