What a grease trap is and how you start one legally

Last updated 2026-08-21

What is a grease trap?

A grease trap is a tank or boxed interceptor on a kitchen drain that slows wastewater so fats, oils, and grease float and food solids sink, instead of coating the public sewer. Most commercial kitchens need one because sewer plants treat FOG as a blockage and interference risk under federal pretreatment rules. ^[1][3]

The name changes by trade. Plumbers say grease interceptor. Health staff say grease trap. Utilities say FOG device. The job does not change.

Hot, greasy water enters a baffled box or a buried tank. Flow drops. Grease cools and rises. Heavier solids drop. The clearer middle layer leaves to the building sewer. Starve that tank of volume, or never pump it, and the grease goes to the street main.

Two hardware families show up on almost every plan review. A hydromechanical grease interceptor is usually a steel or poly box indoors, rated in gallons per minute, often with an external flow control. A gravity grease interceptor is usually a large outdoor tank, rated in gallons, with manholes you can dip. The International Plumbing Code groups these devices in Chapter 10 on traps, interceptors, and separators. ^[5]

I would not buy a used indoor box with a missing rating plate. An inspector wants a listed unit they can match to a standard.

Federal rules never hand you a cute definition of grease trap. They ban the outcome. 40 CFR 403.5(b)(3) prohibits "Solid or viscous pollutants in amounts which will cause obstruction to the flow in the POTW resulting in Interference." ^[1] Cities write FOG ordinances on top of that line.

House kitchens almost never need one. Restaurants, school cafeterias, grocery prep rooms, commissaries, and some church kitchens do. If a fixture sees grease-laden waste, assume you need an interceptor until the building official or the POTW writes otherwise.

FDA Food Code 2022 section 5-402.12 is short on purpose. It says a grease trap, "if used, shall be located to be easily accessible for cleaning." ^[4] Hide it behind a stacked cooler and you will fail the next walk-through.

How do you start a grease trap?

You start at the building desk for the plumbing permit, then you call the sewer utility about its FOG rules. Bring in a plumber who has already pulled interceptor permits on that street. Do not start by buying a tank off a catalog page.

Work in this order. Confirm you are a FOG source under local sewer-use rules. Get the sizing method the city actually uses. Order a listed hydromechanical unit or a gravity tank that matches that method. Pull the plumbing permit, and a FOG or wastewater permit if they issue one. Install it with the vents, cleanouts, and sample access the plan reviewer marked. Get the inspection. Put a pump schedule and a written log in place before the first fryer cycle.

Skip the enzyme bottle as your opening move. Some utilities ban additives that push emulsified grease downstream. That ban is local. Read the ordinance before you buy a case of bottles. ^[10]

Read 40 CFR 403.1 once. It sets the national job as controlling pollutants that pass through or interfere with a POTW or that contaminate sewage sludge. ^[2] Your trap is a tiny piece of that.

I would not sign a construction contract until someone writes the adopted code year and the FOG ordinance section on the proposal. Verbal claims about a "usual 20 GPM box" are how you buy the wrong unit.

Permit fees, review times, and whether a separate FOG registration exists are local. Confirm them with the board that stamps the card. This site does not quote those numbers because they move and they are not national.

EPA's 2004 Report to Congress estimated 23,000 to 75,000 sanitary sewer overflows each year. ^[8] Grease is one of the blockage stories behind that range. That is why the utility asks for a dipstick log.

Who actually regulates grease traps?

Grease traps sit under stacked rules. The plumbing code governs how you install the device. The local FOG or sewer-use ordinance governs how you pump it and what you report. The federal pretreatment framework in 40 CFR Part 403 is what many cities implement when they write those ordinances. ^[2][10] A health department can also ding you on access and sanitation under the Food Code. ^[4]

There is no national grease trap license. Anyone selling you one is selling a myth.

40 CFR 403.8 tells certain POTWs they must run a pretreatment program. ^[10] Clean Water Act section 307, codified at 33 U.S.C. 1317, is the statute behind pretreatment standards. ^[9] EPA's Local Limits Development Guidance is the manual cities use when they turn those duties into numeric limits or BMPs for FOG and other pollutants. ^[12]

Your actual board might be a city utilities director, a county health officer, a state-delegated pretreatment coordinator, or more than one of those desks. Ask who signs the interceptor inspection and who signs the FOG permit. They are not always the same person.

I would keep both phone numbers in the same note on the kitchen wall. When a backup happens at 9 p.m., you want the utility number, not a blog.

If you later buy coverage for a hauling sideline or a multi-site kitchen, the policy questions track these same regulators. Read grease trap guide 11 only after the physical permit path is clear.

How is a grease trap different from a grease interceptor?

In the field, people say grease trap for a small indoor hydromechanical unit and grease interceptor for a large outdoor gravity tank. Model plumbing codes now use interceptor language for both. The job is the same. The pump method, the access, and the paper are not.

A hydromechanical unit is compact, often indoors, and lives or dies by its GPM rating and flow control. A gravity tank is a buried vessel with a long retention time. You dip it through a manhole. You pump it with a vacuum truck.

I use grease trap the way kitchen owners say it, then I switch to the code word the moment I am on a permit form.

Form	Typical rating	Where it sits	Who services it	Paper you show
Hydromechanical interceptor	GPM and grease capacity	Indoors or in a vault	Plumber or pumper	Listing, flow-control spec, indoor log
Gravity interceptor	Gallons of liquid volume	Yard, alley, or parking lane	Licensed pumper with a truck	As-built, manhole access, manifest

Chapter 10 of the International Plumbing Code is the model text most plan reviewers have open. ^[5] Your city may have adopted that code with amendments. Read the amendment sheet. That is where they ban indoor units above a certain seat count, or force a gravity tank for a full-service restaurant.

Buying both just in case is a waste of money. Pick the form the reviewer will approve.

What size grease trap do you need?

You size a grease trap the way your adopted plumbing code and your sewer utility tell you to size it, not the way a catalog sketch tells you. Cities use drainage fixture units, peak flow in GPM, seating counts, or a grease production worksheet. Confirm the method in writing before you order steel or concrete. ^[5]

I would walk the fixture list with the plumber. Pot sinks, woks, tilt skillets, dishwashers (if they are even allowed to discharge to the interceptor), floor drains in the cook line, and prep sinks. Miss one and the unit is undersized on opening day.

Hydromechanical ratings are not a vibe. They come from the test protocol the listing agency used. If the plate is gone, the listing is gone.

Gravity tanks get sized in gallons. A coffee shop and a 200 seat diner do not share a tank size. Anyone quoting a single standard 1,000 gallon tank without fixture data is selling leftover inventory.

EPA pretreatment materials push local limits and BMPs rather than one national gallon chart, which is why two neighboring towns can disagree. ^[3][12]

Waste of money: the smallest indoor box that fits the cabinet when the fryers will blow it out in a week. Also a waste: a giant outdoor tank for a low-FOG bakery because a salesman had one on the truck.

If the utility publishes a worksheet, use that worksheet. Do not freelance a formula you saw on a forum.

What permits and paper come first?

A plumbing permit for the install comes first, plus whatever FOG registration or wastewater discharge permit the POTW requires. Some cities only inspect the plumbing. Some want drawings, a menu, fixture counts, and a signed BMP page.

I cannot quote your fee. Confirm it with the board that takes the check.

Bring the listing sheet, the site plan with the tank or box marked, the venting and cleanout layout, and the sample port if they require one. Food Code access rules still apply after the plumbing inspector leaves. ^[4]

If you remodel an existing kitchen, do not assume the old tank is grandfathered in silence. Many FOG programs trigger a new review when the menu or the seating changes.

Keep the approved plan on site. The first backup will happen when the only copy is in a contractor's email.

Significant industrial users have federal reporting duties under 40 CFR 403.12. ^[11] A normal restaurant is usually not an SIU. You still keep local FOG paper because the ordinance says so, not because you are a chemical plant.

I would not pay a consultant to expedite a simple indoor unit in a city that already publishes a one-page form. That fee is often theater.

How often should you pump a grease trap?

Pump a grease trap as often as your FOG ordinance or your permit says, or sooner if the floating grease and the bottom solids eat the working volume. Many cities write a 25 percent rule, meaning the grease layer plus the solids layer may not take more than about 25 percent of the wetted depth. That figure is a local permit term, not a number I can pin on 40 CFR Part 403. Confirm the percent and the dip method with your utility. ^[10]

Indoor hydromechanical units can need weekly skimming in a heavy fryer shop and still need a full pump on a calendar. Outdoor gravity tanks often sit on 30, 60, or 90 day cycles. Those intervals are not a national schedule. They are whatever the permit or the ordinance printed.

I dip. I do not guess. A wooden stick and a rag tell you more than a contract date.

Regular cleaning and kitchen BMPs are the control that actually works. Dry wipe pans. Catch scrap. Keep the lid closed. ^[12]

If a pumper offers an as-needed route with no written ticket, find another pumper. You need a date, a volume, and a disposal site you can show an inspector.

Overflow into a parking lot or a neighbor's basement will cost more than a year of pumping.

Can you clean a grease trap yourself?

Sometimes you can clean a small indoor grease trap yourself, if local rules allow owner cleaning and you have a legal place to put the waste. Outdoor gravity tanks are a different job. They often meet OSHA's confined space conditions, and 29 CFR 1910.146 is the rule for permit-required confined spaces. ^[6]

Hydrogen sulfide collects in that headspace. OSHA Table Z-2 sets a ceiling of 20 ppm for hydrogen sulfide and a 50 ppm peak for 10 minutes once, if no other exposure occurs. ^[7] People still die in interceptor vaults. I would not put my head in a manhole to save a service call.

If you self-clean an indoor box, use PPE, ventilate, and do not mix the waste with sanitizers or solvents. Put it in a sealed, labeled container your hauler will actually take. Do not pour it in a storm inlet. That is a Clean Water Act problem as well as a local illicit-discharge problem. ^[9]

I hire a licensed pumper for anything with a buried lid. The invoice is cheaper than a rescue.

If staff will be around open vaults, train them to treat the space as a no-entry zone unless a written confined-space program says otherwise. ^[6]

Liability questions after a gassing or a slip land in the insurance stack. For policy shapes that come up around FOG work, see grease trap guide 17 and grease trap guide 23.

What happens to the waste after pumping?

Pumped grease trap waste goes to a renderer, an approved FOG receiving station, or a treatment plant that accepts it. You need a manifest or trip ticket when the city, the state, or the hauler's license requires one. Do not dump it in a dumpster, a fryer-oil barrel, or a storm drain.

Yellow grease from a fryer and brown grease from a trap are not the same commodity. Renderers who pay for fryer oil will often refuse trap sludge. Plan the outlet before the tank is full.

Trap contents are usually not a listed hazardous waste when they are just FOG and food solids. Mix in degreasers, solvents, or unknown shop chemicals and the analysis can change. Confirm characterization with the hauler and the state waste program, not with a forum post.

40 CFR 403.5 also flags petroleum oil and mineral-oil products that cause interference or pass through. ^[1] Do not treat the kitchen interceptor as a used-oil dump.

Keep the ticket. If the receiving plant rejects a load, you want the paper trail, not a memory.

I would not self-haul in a pickup with open drums. That is how you buy a spill and an insurance exclusion. If you still think you will haul, read grease trap guide 29 before you register a truck.

What first-year records should you keep?

Keep the pump log, the manifests, photos of open-tank measurements if your inspector wants them, the interceptor listing or rating plate photo, the as-built, the plumbing permit, the FOG permit if issued, and any sample result the POTW took. First year is when you prove the schedule exists.

Most restaurants are not significant industrial users. 40 CFR 403.12 still matters as the federal reporting skeleton those bigger users live under, and local FOG forms often copy the same instincts: who discharged, when, how much, and where it went. ^[11]

I keep a binder in the office and a one-page log on a clipboard near the unit. Digital photos with dates back up the clipboard when it gets soaked.

If a form set helps you stop inventing columns, GreaseTrapPath publishes a $199 one-time Interceptor + Manifest Kit. Use it only as a blank stack. The city still names the fields.

Do not store the only copy in the manager's personal phone. Staff turnover will erase your year.

Inspectors ask for 90 days or a year. Ask them. Write that retention period on the inside cover. I keep two years because a complaint can arrive late.

When an insurer later asks about prior backups, this same binder is the underwriting file. More on that paper in grease trap guide 35.

What does a grease trap cost in year one?

I will not invent a national install price. Steel indoor units, precast tanks, excavation, traffic control, sampling tees, and permit fees move too much by city and by soil. Budget categories, not a fake sticker: fixture-count or design time, permit, equipment, install, first-year pump contract, and a reserve for a failed inspection.

Ask three plumbers who have pulled interceptor permits on your street, not three internet quotes for a generic grease trap.

Recurring cost is the pump route. A cheap install that needs weekly emergency pumps is not cheap.

Waste of money in year one: enzyme subscriptions, maintenance-free coatings, under-sink units that cannot take the load, and paying a middleman to photocopy the city's own FOG packet.

If you are comparing coverage while you price the physical plant, skim grease trap guide 41. Price the tank first. Insurance does not shrink a 750 gallon hole.

Confirm every municipal fee on the current fee schedule. I will not guess it.

Opening without a pump contract is how you meet the inspector with a full tank and a story.

What insurance and safety issues show up?

The safety issues are hydrogen sulfide, slips on greasy lids, confined-space entry, and a sewer backup into a dining room or a neighbor. The insurance issues follow those facts: general liability for the backup, workers' comp for the crew, pollution or cleanup if you spill a load, and auto if anyone hauls. ^[6][7]

I would not let kitchen staff just hop in an outdoor vault. Write a no-entry rule and mean it.

If you only operate a restaurant and a licensed pumper comes to you, your main gap is often the backup claim and the slip. If you run multiple sites or you touch hauling, the policy stack gets wider. Confirm forms and exclusions with a licensed agent. Nothing here is an insurance offer.

OSHA's confined-space standard is detailed on purpose. 1910.146 expects a program, atmospheric testing, and attendants when the space is permit-required. ^[6] A grease interceptor vault with a single hatch and a bad atmosphere is the textbook picture.

H2S at a 20 ppm ceiling is not a kitchen odor problem. It is a toxic gas limit in Table Z-2. ^[7]

For more insurance-shaped follow-ups in this series, use grease trap guide 47 after you know whether you only cook or you also haul.

What mistakes waste money on day one?

The expensive mistakes are boring. Wrong size. Wrong location. No access. No sample port when the ordinance wants one. Additives instead of pumping. No log. A handshake story that the last owner just had it done.

I would rather delay opening a week than cook into an uninspected, unpumped box. The first overflow that traces to your lateral will not care about your opening-day special. EPA already put the national overflow range on paper in 2004. ^[8]

Do not skip the flow control on a hydromechanical unit to make it drain faster. You just voided the listing.

Do not pave over a gravity-tank lid and then act shocked when nobody can pump it. Food Code access language is there for a reason. ^[4]

If you want a paper stack to mark up before you meet the reviewer, the Interceptor + Manifest Kit is at /start. GreaseTrapPath is an independent publisher, not a law firm and not a service company. Confirm every blank, fee, and interval with the board that actually stamps your job.

Frequently asked questions

What is grease trap?

A grease trap is a plumbing interceptor that holds fats, oils, and grease so they do not coat the public sewer. Commercial kitchens use indoor hydromechanical units or outdoor gravity tanks. Federal pretreatment rules ban viscous pollutants that obstruct a POTW, and local FOG ordinances turn that into a device you must install and pump. House kitchens rarely need one.

How do you start grease trap?

Start with the building department for the plumbing permit and the sewer utility for FOG rules. Get the local sizing method in writing, order a listed unit, install it with required access, pass inspection, then put a pump log in place before you cook. Confirm fees and any separate FOG registration with the board that stamps the card. Do not start by buying enzymes.

Does a small cafe need a grease trap?

Often yes if you have grease-laden fixtures such as a pot sink, grill, or fryer. Seat count is not a free pass. The building official and the POTW decide from the adopted plumbing code and the sewer-use ordinance. Ask both desks before you open. A written exemption beats a verbal maybe from a contractor.

How often do you pump a grease trap?

As often as your permit or FOG ordinance says, or sooner if grease and solids fill the working volume. Many cities use a local 25 percent rule on layer depth. Indoor boxes in heavy fryer shops may need frequent skimming plus a full pump. Confirm the interval and the dip method with your utility. Keep the ticket.

Do enzyme treatments replace pumping?

No. Enzymes and emulsifiers can push grease downstream, which is the opposite of what the sewer plant wants. Some utilities ban them. Pumping removes the mass. Wiping pans and catching scrap cut how fast the tank fills. I would not spend year-one money on a subscription bottle.

What is the 25 percent rule for grease traps?

It is a common local FOG rule, not a federal 40 CFR number. It usually means the floating grease plus the bottom solids should stay under about 25 percent of the tank's wetted depth. Your city may use a different percent or a calendar cycle. Confirm the measurement method on your permit before you argue with a pumper.

Who is allowed to haul grease trap waste?

Usually a licensed liquid-waste or FOG hauler the city or state already recognizes. The load needs a receiving site that accepts brown grease, which is not the same as fryer oil. Some owners may self-clean a small indoor unit if local rules allow it. Buried tanks are a truck job. Keep the manifest.

Does a food truck need a grease trap?

It depends on where you commissary, where you park, and whether you discharge to a sewer. Many commissaries require the truck to dump into the building interceptor, not the street. A mobile unit rarely replaces a fixed trap at the prep site. Confirm with the commissary's utility and the health department before you design a sink.

What if the last owner left no pump records?

Treat the tank as unknown. Dip it, pump it, photograph the empty interior, and start a new log on day one. Ask the utility whether they want a baseline inspection. Do not cook on a handshake story. Inspectors will hold the current operator, not the seller who left town.

Is grease trap waste hazardous waste?

Plain FOG and food solids are usually not a listed hazardous waste. Mix in solvents, unknown degreasers, or shop chemicals and the answer can change. Do not guess from a forum. Ask the hauler and the state waste program how they want it characterized, and keep the ticket that shows where it went.

Can a restaurant owner install a grease trap?

Almost never for a permitted commercial install. Plumbing permits and interceptor listings are why you hire a licensed plumber who has pulled this permit in that city. Owner-install work on a buried tank also walks into confined-space and excavation risk. I would not DIY the unit that keeps you open.

What is a FOG permit?

A local wastewater or sewer-use registration some POTWs issue to food service sites on top of the plumbing permit. It can set pump intervals, BMP pages, and inspection rights. Not every city uses a separate card. Some only inspect the plumbing. Ask the utility which paper they actually stamp.

How long should you keep grease trap manifests?

Keep them as long as the FOG ordinance or your permit says. If nobody printed a period, ask the inspector and write the answer on the binder. I keep two years because complaints arrive late and insurers ask about prior backups. Digital photos of tickets help when the paper gets wet.

Sources

1. eCFR 40 CFR 403.5 Specifically prohibited discharges: Federal pretreatment rules prohibit solid or viscous pollutants in amounts that cause obstruction to POTW flow resulting in Interference, and also address certain oils that cause interference or pass through.
2. eCFR 40 CFR 403.1 Purpose and applicability: Part 403 establishes pretreatment responsibilities to control pollutants that pass through or interfere with POTWs or that may contaminate sewage sludge.
3. U.S. EPA Introduction to the National Pretreatment Program (2011): EPA's national pretreatment program is the federal framework cities use to control industrial and commercial discharges that can interfere with municipal treatment works.
4. FDA Food Code 2022, section 5-402.12 Grease Trap: If used, a grease trap shall be located to be easily accessible for cleaning.
5. ICC International Plumbing Code 2021 Chapter 10 Traps, Interceptors and Separators: The model plumbing code places grease interceptor and separator requirements in Chapter 10, which local governments adopt or amend for sizing and installation.
6. OSHA 29 CFR 1910.146 Permit-required confined spaces: Outdoor grease interceptor vaults often meet OSHA confined-space conditions and, when permit-required, need a written program, testing, and attendants.
7. OSHA 29 CFR 1910.1000 Table Z-2 hydrogen sulfide limits: OSHA Table Z-2 sets a 20 ppm ceiling for hydrogen sulfide and a 50 ppm 10-minute peak if no other exposure occurs.
8. U.S. EPA Report to Congress on the Impacts and Control of CSOs and SSOs (2004): EPA estimated 23,000 to 75,000 sanitary sewer overflows occur each year.
9. 33 U.S.C. 1317 Toxic and pretreatment effluent standards: Clean Water Act section 307 authorizes federal pretreatment standards for pollutants discharged to publicly owned treatment works.
10. eCFR 40 CFR 403.8 Pretreatment program requirements: Certain POTWs must develop and implement local pretreatment programs that become the hook for city FOG ordinances and discharge permits.
11. eCFR 40 CFR 403.12 Reporting requirements for POTWs and industrial users: Federal pretreatment reporting rules for significant industrial users are the skeleton many local FOG logs still copy even when a restaurant is not an SIU.
12. U.S. EPA Local Limits Development Guidance (July 2004): EPA guidance tells POTWs how to set local limits and BMPs, which is why grease trap sizing and pump rules differ by city instead of following one national gallon chart.