What a grease trap is and how you start the work

Last updated 2026-08-21

What is a grease trap?

A grease trap is a plumbing tank that slows kitchen wastewater so fats, oils, and grease (FOG) float and food solids settle, instead of hardening in the public sewer. Cooks still say grease trap. Most modern codes say grease interceptor for the larger outdoor tank. Same job.

FOG cools. Then it sticks. A pipe full of cooled grease is a blockage, and a blockage at the wrong hour is a basement backup or a sanitary sewer overflow. That is the whole reason this device exists.

Federal pretreatment rules do not name your restaurant, but they name the problem. 40 CFR 403.5 tells POTWs to ban "Solid or viscous pollutants in amounts which will cause obstruction to the flow in the POTW resulting in Interference." ^[1] Kitchen grease is the viscous pollutant cities had in mind.

Two hardware families show up on almost every plan review. Hydromechanical grease interceptors sit indoors, often under a sink or in the floor, and they are rated in gallons per minute with a flow-control fitting on the inlet. Gravity grease interceptors sit outside, buried, and they are rated in gallons. They hold wastewater long enough for FOG to rise. Gravity tanks are what most sewer utilities want on a busy dining room.

A grease trap is not a fryer oil caddy. Yellow grease from the vat goes to a renderer. Brown grease from the interceptor is a different waste, with different paper, and it usually cannot ride in the same drum. Do not mix them because a driver said it would be fine.

Remember one physical fact. The unit only works if someone can open it, measure the FOG and solids, and pump it. A tank trapped under a fryer line is a code problem and a health problem. The rest of this guide is the paper path around that tank.

How do you start grease trap work?

You start by naming the job. Installing or replacing a grease trap is a plumbing and building-permit path. Pumping, hauling, and disposing of the contents is a liquid-waste transporter path. Those are different licenses, different trucks, and different boards. Mixing them up is how people buy the wrong tank or the wrong vacuum truck.

If you run the kitchen, make two phone calls on the same morning. Call building and ask which plumbing code they enforce this year (IPC or UPC in most of the country). Call the sewer utility or pretreatment coordinator and ask for the FOG ordinance, the sizing method they will accept, the approved hauler list, and the manifest they want in the file. Write down the person's name. Local rules beat a catalog spec sheet every time. ^[2]

Then hire a licensed plumber who has pulled interceptor permits in that city, more than fixture swaps. Have them draw the unit so lids open without moving a range. FDA Food Code 5-402.12 is blunt: "If used, a grease trap shall be located to be easily accessible for cleaning." ^[4] Cities copy that line into plan review. After install, sign a pumping contract and keep every ticket.

Want to enter the pumping trade? Start at the state environmental agency and the county, not at a truck dealer. Ask which license covers grease interceptor waste. In Wisconsin, servicing grease interceptors sits inside NR 113, the same chapter that covers septage businesses. ^[9] In California, transporters of inedible kitchen grease register with the state under the Food and Agricultural Code. ^[7] Other states use sludge or municipal liquid-waste transporter registrations. Confirm the current form with that board. Nobody here can quote your fee.

Do not buy the vacuum truck until a disposal plant says it will take your waste and tells you the hours, the screening rules, and the ticket format. Then get the vehicle inspected, put the decal on, and buy insurance that actually names pollution and this waste stream. A cheap general-liability binder is not enough. Read grease trap guide 11 before you sign.

Learn confined-space rules on day one. A below-grade interceptor is often a permit-required confined space under OSHA 29 CFR 1910.146. ^[5] People still die in these tanks. You do not hop in because the lid is off.

I would not start this business with enzyme jugs and a pitch about never pumping again. Pretreatment staff have heard it. They still want a pump-out and a manifest. Enzymes are a sideline, not a license.

EPA estimated 23,000 to 75,000 sanitary sewer overflows each year in the 2004 Report to Congress. ^[8] That range is why cities bother you about a tank in the alley.

Is a grease trap different from a grease interceptor?

In the field, people use both words for the same box. In the code book, they are not always the same device. A grease trap usually means the smaller indoor hydromechanical unit. A grease interceptor usually means the larger outdoor gravity tank. Manufacturers blur the words on purpose. Your plan reviewer will not.

The International Plumbing Code puts interceptors and separators in Chapter 10. IPC 1003.1 says interceptors and separators "shall be provided to prevent the discharge of oil, grease, sand and other substances harmful or hazardous to the public sewer, the private sewage system or the sewage treatment plant or processes." ^[3] That sentence is why the reviewer keeps sending your drawing back.

Use this as a working map, then let the local code win.

Kind	Typical site	How it is rated	What it is good for
Hydromechanical interceptor	Indoors, under sink or in the floor	Flow in gpm, often with a flow control	Low-flow prep lines and tight rooms
Gravity grease interceptor	Buried outside	Volume in gallons	Full-service restaurants and hotels
Grease recovery device	Indoors on the waste line	Flow plus an automatic skim	Sites that want less FOG sitting in the tank

A recovery device still needs service. It does not retire the pump schedule. If a salesperson says it does, ask them to put that in writing next to the utility's ordinance. They will stop talking.

I prefer a gravity tank outside when the site can take it. Indoor 20 gpm boxes get undersized, then they get buried under equipment, then they fail a dye test. Cheap on day one. Expensive in year one.

Who actually requires a grease trap?

The city or the sewer utility requires it, using authority that traces back to the Clean Water Act pretreatment program. 40 CFR 403.1 says the federal pretreatment rules implement Clean Water Act duties for discharges into POTWs. ^[6] Large POTWs must run pretreatment programs under 40 CFR 403.8. ^[11] Those programs write the FOG ordinance you will actually live with.

Food service is the usual trigger. Restaurants, school kitchens, grocery prep rooms, hotels, hospitals, and commissaries. Some cities catch food trucks if they hook to a sink inside a commissary. Some catch churches if they run a commercial line. There is no honest national list. The plumbing code plus the FOG ordinance in that service area is the list.

Massachusetts writes interceptor rules into 248 CMR 10, the Uniform State Plumbing Code. ^[10] Other states leave it to the adopted IPC or UPC plus a local sewer bylaw. That split is why a unit that passed in one county fails next door.

A building with only restrooms and a break-room microwave may not need one. A wok line and a dishwasher, you do. Ask pretreatment, not the equipment vendor. Vendors sell tanks.

The health department may also care, because the Food Code wants the trap reachable for cleaning. ^[4] Health and sewer are not the same office. You can pass one and fail the other. Budget time for both stamps.

What paper do you need before you install or pump?

Paper comes in two stacks. One stack is for the building. One stack is for the waste. Starting without both is how you get a red tag or a rejected load at the plant.

For install, expect a plumbing permit, a site plan that shows the interceptor, incoming drain lines, sample port if the utility wants one, and lid locations. Some cities want a sizing worksheet signed by the plumber or engineer. Some want the manufacturer cut sheet and a flow-control detail. Massachusetts reviewers will look at 248 CMR 10. ^[10] IPC cities will look at Chapter 10. ^[3] Do not mail a napkin sketch.

After install, expect an inspection, sometimes a water test, and an approval to discharge. Keep that letter. Pretreatment will ask for it when the first complaint hits the sewer.

For pumping, expect a transporter registration or septage-style license, a vehicle inspection, a decal, driver training records, and a disposal agreement. Wisconsin NR 113 is a clear example of a state chapter that treats grease interceptor servicing as licensed work. ^[9] California registers inedible kitchen grease transporters under Food and Agricultural Code section 19310. ^[7] Your state may use different words. Confirm the form name with the board that prints the decal.

Every load needs a manifest or trip ticket. From, to, gallons, date, signatures. The restaurant keeps a copy. You keep a copy. The plant keeps a copy. If your city uses an electronic FOG portal, that portal is not optional.

GreaseTrapPath has a $199 one-time Interceptor + Manifest Kit at /start if you want a paper bundle in one place. Skip it if the utility already hands you the only forms they will accept. We do not stamp permits.

Hauler insurance certificates show up on this stack too. Utilities ask for them. See grease trap guide 17 and grease trap guide 23 for the coverage names people actually get asked about. Confirm limits with the utility, not with a forum post.

How do you size a grease trap?

You size it the way the authority having jurisdiction tells you to size it. That is a boring sentence and it is the only one that will pass plan review. National myths about "20 gallons per seat" die in the first comment letter.

Hydromechanical units are sized on flow, in gpm, with a flow-control fitting that keeps the tank from being blown out during a rush. Gravity tanks are sized on volume and detention time so FOG can rise. The IPC interceptor chapter is the usual starting text in IPC states. ^[3] Some utilities overlay their own worksheet that counts fixtures, dishwashers, wok ranges, and hours of operation.

A dishwasher changes the math. Hot emulsified grease sails through an undersized indoor box and congeals in the street main. If the site has a hot dish machine, I want the gravity tank and I want the dish line included, unless the utility has a written exception. Get that exception on letterhead.

Do not let the kitchen designer shrink the unit to save floor space. The savings land on you the first time pretreatment pulls a sample and the effluent is a milkshake. Oversizing a buried tank is usually cheaper than a year of notices of violation.

If two methods conflict, the stricter local method wins. Ask the reviewer which worksheet to attach. Then attach only that one. Extra math from a blog does not help.

How often should a grease trap be pumped?

As often as your FOG ordinance says, or sooner if FOG plus settled solids hit the local trigger. Many utilities use a 25 percent rule. When grease and solids fill about a quarter of the wetted volume, you pump. That 25 percent figure is a local ordinance habit, not a number in 40 CFR 403. ^[1] Confirm the trigger in writing.

Some cities also set a maximum interval. 30, 60, or 90 days shows up a lot on small indoor units. Large gravity tanks may run longer if measurements stay under the trigger. Nobody has a clean national data set on the right number of days. The closest thing you will get is your utility's enforcement file.

Measure. Do not guess from the calendar. A dipstick or a sludge judge and a written log beat a verbal "it looked fine." Inspectors have heard "it looked fine" all week.

Pumping less to save money is how you pay more. A collapsed line, a weekend plumber, and a closed dining room cost more than a scheduled vacuum truck. If you haul, build the interval into the contract so the restaurant cannot skip this month without a signature.

Insurance and downtime sit next to this question. A backup into a dining room is a claim. Read grease trap guide 29 if you are trying to guess which policy even answers that call.

What federal rules apply to grease traps?

The federal rule you can actually quote is the pretreatment prohibition on sewer-clogging waste. 40 CFR 403.5 is the section. ^[1] 40 CFR 403.1 is the purpose statement that ties that prohibition to the Clean Water Act. ^[6] 40 CFR 403.8 is why a big city has a pretreatment coordinator who can fine the kitchen and the hauler. ^[11]

EPA's Introduction to the National Pretreatment Program (EPA-833-B-11-001) is the staff manual behind those sections. It explains how POTWs must keep interference and pass-through out of the plant. ^[2] FOG control programs are how cities do that for restaurants.

There is no federal grease-trap license for a diner. There is no federal pump-out interval. There is no federal tank size. People who talk like there is are selling something.

OSHA is the other federal book that hits this work. 29 CFR 1910.146 is the permit-required confined space standard. ^[5] OSHA defines an oxygen-deficient atmosphere as any atmosphere containing less than 19.5 percent oxygen by volume. Interceptors go there fast when FOG is rotting. Atmospheric testing, a permit, an attendant, and rescue gear are the job. They are not optional because the tank is only five feet deep.

If you transport waste across state lines or into a plant that treats it as a special waste, more rules can stack on. Those are state and plant rules. Read them. Do not assume brown grease is ordinary trash.

Can you climb into a grease trap to clean it?

Not as a casual move. A below-grade interceptor is often a confined space, and it is often permit-required once you add a hazardous atmosphere, engulfment, or a layout that blocks exit. OSHA 29 CFR 1910.146 is the rule. ^[5] Hydrogen sulfide and low oxygen are the usual killers. The waste looks like mud. The air is not mud.

OSHA sets the oxygen-deficient atmosphere threshold at 19.5 percent oxygen in 29 CFR 1910.146. ^[5] If you cannot test the air, you do not enter. If you do not have a written program, an attendant, and a way to get a body out, you do not enter. Vacuum it from the top.

I would fire a crew that hops in to push a wand. That habit has a body count. Top-side pumping is slower and it is the correct default.

If your business model needs entry for repairs, build a real confined-space program before the first job. Training, calibrated meters, retrieval, and a host employer process when you work on someone else's property. Your insurer will ask. So will OSHA after an incident. grease trap guide 41 is the next read if you are mapping that risk to a policy, not a pep talk.

Where does grease trap waste go?

It goes to a plant that is allowed to take brown grease or mixed interceptor waste. That may be a publicly owned treatment works with an approved receiving station, a dedicated FOG facility, or a renderer if the load meets that plant's spec. It does not go into a ditch, a storm drain, a dumpster, or a farm field because someone offered cash.

Yellow grease from fryers is a commodity. Brown grease from traps is a waste. Keep them apart on the truck and on the ticket. California even built a separate inedible kitchen grease transporter registration around that distinction. ^[7] Other states bury the same idea in sludge or liquid-waste rules. ^[9]

Call the plant before the first route. Ask about screening, grit, pH, appointment windows, and what happens if the load is mostly water. Some plants bounce dilute loads. Some charge more. Get the rejection rules in writing so you are not arguing at the scale house with a full tank and a hot afternoon.

Illegal dumping is the fastest way to lose the decal. It is also how cities justify sting operations on haulers. If a restaurant asks you to hit the creek, you leave. Keep the text.

Disposal cost moves. It is a local tipping fee, not a national tariff. Confirm it with the plant you will actually use. Anyone quoting you a single US price is guessing.

What does first-year grease trap work cost?

Nobody publishes a clean national price. Anyone who gives you one number for a grease trap is mixing a $12 gasket with a $40,000 buried tank and calling it research.

Hardware quotes in the trade run from low four figures for a small indoor hydromechanical unit up to tens of thousands for a large buried gravity interceptor plus excavation, traffic plates, and restoration. I cannot certify a current bid from this desk. Get three local quotes. Add the plumbing permit, which is a city fee you confirm on the permit counter page, not here.

If you are the hauler, first-year cash goes to the truck, tanks, hose, the state or county license, vehicle inspection, disposal accounts, and insurance. Insurance is not the place to go cheap. Pollution, auto, and the utility's additional-insured demand will show up. grease trap guide 53 and grease trap guide 65 are worth a click before you accept a binder that names the wrong operations.

Pumping for the restaurant is a service contract. Price it on gallons and interval, not on hope. Build in after-hours callouts. The first grease backup will be Saturday night.

Waste of money, in my view: miracle additives sold as a substitute for pumping, unrated homemade boxes, and buying a truck before a plant accepts your waste. Spend on access, sizing, and paper instead.

What should you confirm with the board before you spend money?

Confirm the code edition, the FOG ordinance, the sizing worksheet, the approved interceptor list if they have one, the hauler license name, the current fee, the inspection sequence, and the manifest format. Confirm whether indoor hydromechanical units are even allowed on a full-service kitchen. Confirm confined-space expectations if your crews enter. Confirm the disposal plant.

Do not trust a national blog for a fee or a processing time. Those change. GreaseTrapPath is not a law firm and not a service company. We do not get you approved. The board that stamps the card is the only clock that counts.

Want forms gathered in one packet? The $199 Interceptor + Manifest Kit is at /start. If the city already publishes the only ticket they will file, use theirs.

Then keep a folder. Permit, approval letter, as-built, pump tickets, hauler license copy, insurance cert. That folder is the job. The tank is just steel or concrete. For the coverage side of that folder, grease trap guide 77 is a reasonable next stop.

Frequently asked questions

What is grease trap?

A grease trap is a tank on a kitchen drain that slows wastewater so fats, oils, and grease float and solids settle. The cleaner water then goes to the sewer. Codes often call larger outdoor tanks grease interceptors. The job is the same: keep FOG out of the public pipe. Local plumbing and FOG rules decide when you must have one.

How do you start grease trap?

Name the work first. Kitchens start with the building department and the sewer utility, then a licensed plumber, a permit, and a pumping contract. Haulers start with the state or county transporter or septage license, a disposal plant that will take the waste, a legal truck, and confined-space rules. Confirm every form and fee with that board before you buy equipment.

Do I need a permit to install a grease trap?

Almost always yes, as a plumbing permit plus whatever the sewer utility adds. Plan reviewers will want the sizing method they recognize, lid access, and often a sample port. IPC Chapter 10 or the locally adopted plumbing code is the usual text. Confirm the current submittal checklist with the building department that will inspect it.

How often do you empty a grease trap?

On the interval in your FOG ordinance, or sooner if FOG and solids hit the local trigger. Many utilities use a 25 percent full rule. Some also cap indoor units at 30, 60, or 90 days. There is no honest national day-count. Measure the layers and keep the tickets. Confirm the trigger with pretreatment.

Can I clean a grease trap myself?

A restaurant can often contract any licensed hauler, and a few cities still allow the owner to pump a small indoor unit if they haul to an approved plant with a manifest. You should not enter a below-grade tank without a confined-space program. Dumping the waste in a trash can or a storm drain is illegal. Ask the utility what self-clean really means there.

What is the 25 percent rule?

It is a common local FOG rule, not a number inside 40 CFR 403. When floating grease plus bottom solids take up about 25 percent of the tank's wetted volume, you schedule a pump-out. Some cities write it into the ordinance and inspect with a dipstick. Confirm whether your utility uses it and how they want it written on the ticket.

Is grease trap waste hazardous waste?

Usually it is handled as special, liquid, or interceptor waste, not as listed hazardous waste. Plants still set pH, screening, and appointment rules. Do not mix it with yellow fryer oil. Do not guess. The receiving facility and your state transporter rules decide the label on the manifest. Ask both before the first load.

What size grease trap do I need?

The size your plan reviewer will stamp. Hydromechanical units are in gpm. Gravity tanks are in gallons. Fixture counts, dishwashers, and hours of operation change the worksheet. A national seat-count rumor is not a method. Use the utility's form or the adopted plumbing code method, and attach only that.

Do enzyme treatments replace pumping?

Not for compliance in any city I would trust. Additives may change odors or move grease downstream, which can make the sewer problem worse. Pretreatment still wants a measured pump-out and a manifest. Spend the additive money on access lids and a real hauler contract. If a vendor claims a waiver, get the utility to say so on letterhead.

What is brown grease vs yellow grease?

Yellow grease is used fryer oil, a renderer commodity if it stays clean. Brown grease is the mixed FOG and food solids from a grease trap or interceptor. Different plants, different paper, different trucks in many states. Mixing them can get a load rejected and can violate a transporter registration. Keep the streams and the tickets apart.

Do I need a license to pump grease traps?

In most states yes, under a septage, sludge, liquid-waste, or inedible kitchen grease transporter program. Wisconsin NR 113 and California Food and Agricultural Code section 19310 are two written examples. The restaurant's business license is not a hauler license. Confirm the exact credential name and current fee with the issuing board.

Can a food truck skip a grease trap?

Sometimes on the truck itself, almost never at the commissary sink that actually drains to the sewer. If the truck discharges to a public system or a shared prep site, that site's interceptor rules apply. Street vending rules and plumbing rules are different offices. Ask both. Do not take a vendor's mobile units are exempt line as law.

Sources

1. eCFR, 40 CFR 403.5 National pretreatment standards: Prohibited discharges: Federal pretreatment rules prohibit solid or viscous pollutants in amounts that will cause obstruction to POTW flow resulting in Interference.
2. U.S. EPA, Introduction to the National Pretreatment Program (EPA-833-B-11-001, 2011): EPA's pretreatment manual explains how POTWs implement Clean Water Act controls on commercial and industrial discharges, including interference from sewer-clogging waste.
3. ICC, International Plumbing Code 2021 Chapter 10 Traps, Interceptors and Separators: IPC 1003 requires interceptors and separators to prevent oil, grease, sand, and other harmful substances from entering the public sewer or treatment plant.
4. U.S. FDA, Food Code 2022 section 5-402.12 Grease Trap: FDA Food Code 5-402.12 requires that if a grease trap is used, it shall be located to be easily accessible for cleaning.
5. OSHA, 29 CFR 1910.146 Permit-required confined spaces: OSHA defines an oxygen-deficient atmosphere as less than 19.5 percent oxygen by volume and sets permit-required confined space duties that apply to many below-grade interceptors.
6. eCFR, 40 CFR 403.1 Purpose and applicability: 40 CFR Part 403 implements Clean Water Act pretreatment requirements for discharges into publicly owned treatment works.
7. California Food and Agricultural Code section 19310: California requires transporters of inedible kitchen grease to be registered with the Department of Food and Agriculture.
8. U.S. EPA, Report to Congress on CSOs and SSOs (EPA 833-R-04-001, 2004): EPA estimated 23,000 to 75,000 sanitary sewer overflows per year and 3 to 10 billion gallons of untreated wastewater released annually from SSOs.
9. Wisconsin Legislature, NR 113 Servicing Septic Tanks, Holding Tanks, Grease Interceptors: Wisconsin NR 113 licenses businesses that service grease interceptors and other septage tanks and sets operating rules for that work.
10. Massachusetts, 248 CMR 10.00 Uniform State Plumbing Code: Massachusetts writes interceptor and plumbing installation rules into 248 CMR 10, which local inspectors enforce on grease-trap installs.
11. eCFR, 40 CFR 403.8 Pretreatment program requirements: Certain POTWs must develop pretreatment programs that enforce prohibited-discharge standards against commercial users.
12. eCFR, 40 CFR 403.3 Definitions: Federal pretreatment rules define POTW as a publicly owned treatment works, the sewer authority that writes local FOG ordinances.