Grease Trap Pumping: Cleaning Frequency, Records and How It Differs From Septic Pumping

A grease trap or interceptor is a different device from a septic tank. In the City of Spokane, hydromechanical interceptors must be cleaned at least every 30 days, or when 25 percent full, and gravity interceptors every 90 days. Records are kept for three years, and Idaho DEQ says grease trap waste is not domestic septage.

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Last reviewed: October 26, 2026

What a grease trap is

A grease trap, also called a grease control device or grease interceptor, is a unit that catches fats, oils and grease from kitchen wastewater before it reaches a sewer or an on-site system. Spokane County's grease control device policy describes the purpose: devices designed to remove fats, oils and grease and food solids from wastewater, installed where sinks, floor drains, dishwashers and other fixtures in commercial businesses are plumbed to the sanitary sewer. It lists restaurants, cafes, catering facilities, commissaries, hotels, cafeterias, convenience stores, full-service grocery stores, schools, hospitals and food manufacturing facilities as the type of facility concerned.

A grease trap is not a septic tank. A septic tank treats household sewage and is a part of an on-site sewage system. The grease device catches kitchen grease and food solids upstream. A business may have both, and each is pumped on its own interval by its own rules. This page covers the grease device. For septic tanks, see septic pumping.

Two types of device in Spokane

The county policy dated March 11, 2026 defines two common types. Hydromechanical grease interceptors can be inside or outside the facility, may contain weirs or diffusers, and are required to have flow restrictors. Gravity grease interceptors are larger, and the policy describes fixtures such as dishwashers and prep sinks being plumbed to them. The policy says facilities with 40 or fewer seats and 40 or fewer meals per peak hour use a hydromechanical interceptor, and larger facilities use a gravity interceptor. Oil/water separators and sand traps are a separate category, for repair garages, car washes and similar sites.

Cleaning frequency in the City of Spokane

Spokane Municipal Code 13.03.0508 sets the interval. Grease control devices, oil/water separators and sand traps must be cleaned often enough to prevent objectionable odors, surcharge of the device, obstruction, or interference with the sewer system.

The Wastewater Director may grant an exception where the user shows that a less frequent interval will keep the device below 25 percent full. The code also says the cleaning must be done by pumping the device dry and washing the sides, baffles and tees to remove sludge on all surfaces. Water removed during cleaning may not be returned to the device or to the downstream sewer. Chemical or biological additives, enzymes and surfactants acting as grease emulsifiers are not permitted as a cleaning method.

These are City of Spokane rules. Other cities and sewer districts have their own, and the policy cited above is from Spokane County. A business outside Spokane should ask its sewer utility or, if it is on a septic system, the health district.

Records

The City code says users with a grease control device must keep records on site for at least three years showing that it has been maintained and cleaned as required, along with the date and time material was removed, the volume removed, and the name of the hauler or disposal company. The City's recordkeeping sheet lists the fields: hauler name, address and phone; date and time of service; business name and address; location, size and type of each device; approximate quantity of grease and food waste in gallons, inches or percent; pumping frequency; details on structure, maintenance or repairs; and grease disposal. It also says a separate log is needed for each device. The City may inspect, and the user must make the device and the records available.

Grease trap waste is not septage

Idaho DEQ defines domestic septage as material removed from septic tanks, cesspools, portable toilets, privy vaults, holding tanks, RV tanks and similar facilities receiving wastewater strictly from domestic sources. It says domestic septage does not include material from septic tanks, holding tanks or similar works that receive commercial or industrial waste, and names grease trap waste as an example. That is why septic pumpers and grease haulers can be different companies with different approvals. Ask the hauler where the waste goes and whether the hauler is approved for it.

Restaurants on septic systems

Some food service establishments are served by on-site sewage systems instead of a sewer. WAC 246-272A-0275 says the local health officer shall require annual inspections of on-site systems serving food service establishments and may require pumping as needed. A grease device ahead of the septic tank is not the same as the tank. Pumping the grease device does not satisfy the inspection or pumping of the tank.

Home kitchens

Homes do not usually have grease interceptors. The advice for homes comes from EPA, which says not to pour grease such as fats, butter, wax, cheese or heavy cream down the drain, and the Washington Department of Health, which notes that oil and grease float to the top of a septic tank and form the scum layer. Every gallon of grease in a house tank adds to the layer that can reach the outlet baffle. See septic tank cleaning.

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What changes the price

This site does not quote prices. Device size, frequency, access, distance and disposal all change the price of a grease service. A device that has to be cleaned every 30 days costs more over a year than one cleaned every 90 days.

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Frequently Asked Questions

How often must a grease trap be cleaned in Spokane?

Under Spokane Municipal Code 13.03.0508, hydromechanical grease interceptors must be cleaned at least once every 30 days, or sooner when 25 percent full of grease or settled solids. Gravity interceptors must be cleaned by a wastewater hauler at least every 90 days, or sooner at 25 percent.

How long must grease trap records be kept?

At least three years, on site. The City of Spokane's recordkeeping sheet lists hauler name, service date, device location, size and type, approximate quantity removed, pumping frequency, repairs and disposal. A separate log is required for each device, and records must be available for inspection.

Is grease trap waste the same as septic tank waste?

No. Idaho DEQ says domestic septage does not include material from septic tanks, holding tanks or similar works that receive commercial or industrial waste, and names grease trap waste as an example. Grease haulers and septic pumpers can be different companies with different approvals.

Can I use enzymes or additives instead of pumping a grease trap?

Not in the City of Spokane. Municipal Code 13.03.0508 says chemical or biological additives, enzymes or surfactants acting as grease emulsifiers are not permitted as a method for cleaning a grease control device. Cleaning means pumping the device dry and removing sludge from all surfaces.

Does a restaurant on a septic system need inspections?

Yes. WAC 246-272A-0275 says the local health officer shall require annual inspections of on-site sewage systems serving food service establishments and may require pumping as needed. Contact the health district, SRHD in Spokane County, about the requirements for the tank.

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