Grease Trap & FOG Compliance FAQ

A grease trap is a plumbing device installed between a commercial kitchen and the municipal sewer. It uses gravity and residence time to separate fats, oils, and grease (FOG) from wastewater before it enters the sewer system. FOG floats to the top of the trap, solids settle at the bottom, and cleaner water exits through a middle outlet.

The terms are often used interchangeably, but plumbing codes distinguish by size and flow rate. A grease trap is typically a smaller under-sink or point-of-use unit rated under 50 gallons per minute. A grease interceptor is a larger in-ground or exterior vault holding 500 to 5,000 gallons, used by full-service restaurants and institutional kitchens.

Yes, if your establishment produces FOG — which includes almost any food service operation with a commercial kitchen, fryers, grills, dishwashers, or 3-compartment sinks. Exemptions sometimes apply to coffee shops, ice cream parlors, and prepackaged food retailers. Verify with your local wastewater authority and plumbing inspector before assuming you are exempt.

FOG stands for fats, oils, and grease. It refers specifically to lipids that are liquid at kitchen temperatures but solidify as they cool in sewer pipes. FOG includes cooking oils, animal fats, butter, dairy cream, mayonnaise, and salad dressings. Regular kitchen solids (food scraps, bones, paper) are a separate solid waste stream and should never enter a grease trap.

Grease trap sizing depends on your plumbing code (IPC or UPC), your peak drainage flow rate, and your local ordinance. Under the IPC, traps are sized based on drainage fixture unit counts. Under the UPC, they are sized with a formula based on fixture load and a retention factor. Most cities require a minimum of 20 gallons per minute (GPM) for under-sink traps and 1,000 gallons capacity for in-ground interceptors at full-service restaurants. Our free sizing calculator handles both methods.

On the drain line between grease-producing fixtures and the building sewer, in an accessible location. Under-sink traps go directly below 3-compartment sinks and pre-rinse stations. In-ground interceptors typically sit in a parking lot, alley, or basement mechanical room with manhole access for pumping. Never connect toilets, urinals, or storm drains to a grease trap.

No — grease trap installation requires a licensed plumber in nearly every US jurisdiction. Most cities also require a plumbing permit, inspection, and sign-off by the local plumbing authority before the trap can be placed in service. Improper installation is a common violation and a frequent cause of failed health inspections.

The International Plumbing Code (IPC) and Uniform Plumbing Code (UPC) are two model plumbing codes adopted by US states. The IPC (used by about 35 states including Texas, New York, and Georgia) sizes grease interceptors based on drainage fixture units. The UPC (used by California, Washington, Oregon, and others) uses a different formula with fixture load and retention factors. Your state plumbing code determines which method applies.

Most US cities require pumping every 90 days. More strict jurisdictions (Houston, much of Florida, parts of Los Angeles County) require pumping every 30 days for high-volume restaurants. Some cities allow up to 180 days or annual pumping for low-FOG establishments like bakeries and coffee shops. Always pump earlier if you hit the 25 percent rule, regardless of your schedule. See our 25/50 rule guide for details.

The 25 percent rule requires restaurants to pump their grease trap before the combined FOG and settled solids reach 25 percent of the total liquid depth. This is a hard ceiling enforced by inspection. Exceeding it triggers fines and a mandatory emergency pump-out in most cities.

Some jurisdictions add a 50 percent rule on settled sludge — the solids layer at the bottom of the trap cannot exceed 50 percent of total liquid depth before pumping is required. The combined 25/50 rule ensures both FOG buildup and solids accumulation trigger pump-outs.

A licensed grease hauler. Most US cities require haulers to register with the local wastewater utility, maintain a permit, and provide a manifest at every pump-out. Do not use uncertified "cash" haulers — they often illegally dump FOG and can trigger liability for the restaurant. Ask the hauler for their city license number and a copy of their insurance.

Pumping costs vary by trap size and region. Under-sink HGIs (20 to 50 gallons) typically run $150 to $400 per service. In-ground interceptors (1,000 to 2,000 gallons) usually cost $250 to $600 per pump-out. Larger interceptors (3,000+ gallons) can run $600 to $1,200. Prices are higher in urban markets and lower in rural areas. Always get a written estimate including disposal fees.

Permit requirements vary by city. Roughly half of US cities in our database require a separate FOG permit with annual fees ranging from $50 to $500. The other half regulate grease traps through the plumbing permit and ongoing inspections without a separate FOG permit. Check your city's specific rule in our regulations database.

Fines range from $100 per day in smaller jurisdictions to $25,000+ per day under federal Clean Water Act violations. Typical first-offense fines are $500 to $2,500. Repeat violations, causing a sanitary sewer overflow, or discharging FOG to storm drains can trigger felony-level penalties in extreme cases.

Local wastewater utility inspectors — often called FOG inspectors, pretreatment inspectors, or sewer compliance officers. Some cities use third-party contractors. Health department inspectors also check grease traps during routine restaurant inspections. Both scheduled and surprise inspections are standard practice.

Most cities require you to keep pumping manifests, hauler licenses, and inspection reports for 3 to 5 years. Some require a bound logbook kept on-site showing every cleaning event, the hauler name, date, volume pumped, and disposal destination. Missing records is itself a compliance violation in most jurisdictions.

Immediately stop operations, contain the overflow, and call a licensed hauler for emergency pump-out. Notify your local wastewater utility within 24 hours — most cities require self-reporting of any FOG discharge. Document everything. Overflows reaching storm drains or waterways trigger EPA notification requirements and potentially significant penalties.

Most US cities explicitly prohibit the use of emulsifiers, enzymes, bacteria, solvents, or degreasers that liquefy FOG and cause it to pass through the trap. These additives give the appearance of a clean trap but simply push FOG into the sewer where it re-solidifies. A few jurisdictions allow specific bioremediation products certified by the local utility. Check your city's ordinance before using any additive.

BMP stands for Best Management Practices — the staff training and operational procedures that reduce FOG at the source before it reaches the grease trap. Standard BMPs include scraping plates into trash before dishwashing, wiping greasy pans before rinsing, installing strainers on all drains, cold-water-only dishwashing pre-rinse, and never pouring cooking oil down drains. Many cities now require documented BMP training programs.

Most jurisdictions prohibit connecting commercial food waste disposers (garbage grinders) upstream of a grease trap. The ground food increases solids load, fills the trap faster, and can clog the flow control device. Some cities allow disposals only with a larger interceptor sized for the additional load. Verify before installation.

Typical connections: 3-compartment sinks, pre-rinse stations, wok stoves, tilt skillets, dishwashers, floor drains in cook lines, and mop sinks. Connections generally prohibited: toilets, urinals, hand-wash sinks, restroom floor drains, storm drains, and clean-water equipment like ice machines. Local plumbing code and ordinance determine final connection rules.