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City of Paso Robles
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Wastewater Division Treatment Plant
3200 Sulphur Springs Road
Paso Robles, CA 93446
(805) 237-3865
(805) 237-3886 FAX
Mon-Fri 7am to 3:30pm


In the wastewater collection and treatment business, grease is a big problem! Grease is singled out for special attention because of its poor solubility in water and its tendency to coat surfaces. Warm grease is liquid and may not appear harmful, but as the liquid cools and the grease congeals, it may stick to surfaces, which may cause sewage backup or a treatment plant process upset.

Oil and grease in wastewater can accumulate in sewer pipes and at the wastewater treatment plant, requiring increased cleaning and early replacement.

Typical grease-producing commercial/manufacturing entities (such as restaurants) are required to install preliminary treatment facilities commonly known as grease traps or interceptors at drains where grease typically accumulates.

PDF Document Download Grease Device Booklet - Keeping Fats, Oils, and Grease Out of the Sewer Questions and Answers for Food Service Establishments regarding Fats, Oil, and Grease and Grease Removal Devices

What is a Grease Trap and how does it work?
A grease trap is a small reservoir built into the drains a short distance from the grease producing area. Baffles in the reservoir slow down the wastewater flow and reduce turbulence allowing the grease and water to separate. Grease naturally rises to the surface, and the trap system retains the grease while providing for the grease-free wastewater to continue flowing into the sewer system. The grease must be removed from the trap periodically.

Do I need a Grease Trap?
If you have a commercial kitchen and are washing dishes, you probably need a grease trap. Even foods that are not fried contain a lot of grease. Grease is washed down the drain when dishes are washed and must be contained. Residences do not need a grease trap. City code and industry standards do not require grease traps for individual dwelling residences. It is required of all establishments that produce large amounts of grease such as restaurants, institutional and commercial kitchens and other similar operations.

Is the Grease Trap I have adequate?
The size is largely determined by your maintenance schedule. If you have to clean it more often than you think you should, then chances are you need a bigger grease trap. Typically, a restaurant will require between a 50 lb. and a 100 lb. grease trap depending on food being prepared, and the number of customers served.

Things you should know when sizing a Grease Trap/Interceptor
It is extremely difficult to formulate exact criteria for sizing grease traps because of the many variables that exist. Where one grease-producing establishment may burn grease it generates, another may use a grill and collect its grease for disposal; no two are operated in the same manner. The size of the grease trap required by the city is the minimum allowable size* and may require frequent cleaning to operate properly.

* Interceptors/traps must be sized using the uniform plumbing code to have a capacity sufficient to provide the appropriate quality of effluent as per city discharge standards.

Other considerations are:

  • Type of food being prepared (fried, baked, broiled, deep fat fried, etc.)
  • Seating capacity or quantity of wastewater flow.
  • Retention time required for efficient grease trap operation.
  • Frequency of maintenance.
  • Accessibility of trap for maintenance.
  • Location of trap as close to the grease producing area as possible. It must also be installed so no sanitary waste from a toilet will be collected in the grease trap.
  • Garbage grinders may not be routed through a grease trap.
  • Installing the trap outside the facility is a very smart idea.

Am I part of the problem or the solution?
One of the most important things to remember is that if you have a grease trap, maintain it properly. Work out a specific cleaning schedule right for you and your establishment. All grease traps/interceptors need to be cleaned out periodically.

How can I be sure I am in compliance with the rules?
Contact the City’s Wastewater Division, they will be happy to come and inspect the grease trap and let you know whether it is being properly maintained.

How do I clean my Grease Trap/Interceptor
The following procedure is recommended:

For small traps under counters:

  • Bail out any water in trap to facilitate cleaning.
  • Remove the accumulated grease out of the trap. Be sure to scrape the baffles, sides and lid.
  • Deposit the grease in a watertight container and have a rendering/tallow company pick it up.

For large underground traps/interceptors:

  • You will likely need to hire a professional cleaning company with the necessary equipment and experience for the job.
  • Frequent trap cleaning reduces the grease loading and shortens cleaning time.

Do not:

  • Flush out with hot water
  • Use drain cleaners, enzymes or bacteria agents.

What will be the criteria for Grease Trap inspections?
All grease-producing establishments will be inspected using the following criteria:

Percent of trap filled
< 25%
> 50%
Trap Condition

If the trap is in fair condition the City will advise increasing the cleaning schedule; if the trap is in poor condition, the City will issue a correction order to clean the trap and increase the future maintenance frequency.

Can you recommend a maintenance schedule?
All grease traps should be cleaned at least once per month, although some establishments will need to clean their traps more often. If you clean your grease trap too often, then consider installing a larger trap.

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