What Is a Fatberg? How Cooking Oil Contributes to Sewer Blockages

A fatberg is a dense sewer blockage formed when fats, oils, and grease combine with wet wipes and other materials that do not break down properly. These materials collect inside pipes and sewer lines, gradually restricting the flow of wastewater.

Cooking oil is one part of the problem, but it is not the only cause. Fatbergs usually develop from a mixture of household grease, personal care products, food residue, and non-flushable waste.

The good news is that home cooks can help prevent them through simple habits. Keeping used cooking oil out of drains, scraping plates before washing, and placing wipes in the trash all reduce the amount of material entering the sewer system.

What Is a Fatberg?

A fatberg is a mass of congealed fats, oils, and grease mixed with wet wipes, paper products, and other waste that does not break down easily in a sewer. The material accumulates in layers, narrows the available space inside the pipe, and may eventually block wastewater flow.

The term combines the words “fat” and “iceberg.” It is commonly used for larger masses found in public sewer systems rather than for ordinary household drain clogs. New York City describes fatbergs as masses of congealed grease and personal hygiene products that remain in sewer systems.

What Is a Fatberg Made Of?

Fatbergs are not made from one material. They form when sticky fats, oils, and grease collect other waste moving through a drainage or sewer system.

The grease provides a surface that other materials can cling to. Wipes, food particles, paper towels, hygiene products, and other non-flushable items add structure and volume to the growing blockage.

This combination explains why preventing fatbergs requires attention in both the kitchen and the bathroom.

Fats, Oils, and Grease

Wastewater agencies commonly group kitchen fats under the term FOG, which stands for fats, oils, and grease.

Household examples include:

• Used frying oil

• Bacon grease

• Meat drippings

• Butter and margarine

• Lard and shortening

• Greasy sauces and gravy

• Fat left after roasting or sautéing

These materials do not behave like ordinary wastewater. They may cool, thicken, stick to plumbing surfaces, or combine with residue already inside a pipe.

Liquid oils matter too. Vegetable oil and olive oil may remain liquid in the kitchen, but they can still coat pipes and help trap food debris. Seattle Public Utilities advises residents to keep cooking oils and grease out of home drains because they can stick to pipes and build up over time.

Wipes and Other Non-Flushable Materials

Wet wipes are another major part of many fatbergs.

A product may pass through the toilet bowl without breaking down quickly inside a sewer. That means the word “flushable” on a package does not necessarily mean the product will move safely through household plumbing, public sewers, and wastewater treatment equipment.

The U.S. Environmental Protection Agency identifies fats, oils, grease, and household products such as some wipes among the inappropriate materials that can clog sewer systems. New York City also instructs residents to place all wet wipes in the trash, including those marketed as flushable.

Other materials that should stay out of toilets and drains include:

• Paper towels

• Facial tissues

• Sanitary products

• Cotton swabs

• Dental floss

• Cleaning wipes

• Food scraps

Toilet paper is designed to break apart in water. Many other household products are not.

How Are Fatbergs Formed?

Fatbergs generally form through gradual buildup rather than one isolated disposal mistake.

The process may look like this:

1. Fats, oils, or grease enter a household drain.

2. Some of the grease clings to the pipe or settles farther along the system.

3. Food particles and other debris stick to the greasy coating.

4. Wipes and non-flushable materials enter from toilets or other drains.

5. The materials collect and become more compact.

6. Additional layers continue forming.

7. Wastewater has less room to move through the pipe.

Over time, this buildup can restrict flow, contribute to backups, and require sewer maintenance.

Not every small amount of grease instantly creates a fatberg. The concern is the repeated disposal of oil, grease, wipes, and other unsuitable materials into the same connected system.

From a Kitchen Drain to a Sewer Line

Wastewater leaving a kitchen sink first travels through the home’s plumbing. It then moves through a private sewer lateral or building line before reaching the public sewer system.

Grease can cause trouble at more than one point along this route. Inside a home, it may contribute to a slow drain or kitchen clog. Farther along, grease and debris may restrict a building line. In the public sewer, material from many properties can combine and create a larger blockage.

Seattle Public Utilities explains that grease and debris can slow or completely block a side sewer, which connects private plumbing to the public system.

What Role Does Cooking Oil Play in Fatbergs?

Cooking oil acts as a contributing material and binding surface. When oil enters a drain, it does not dissolve into the water. Some may move through the system, while some may remain as a greasy coating on pipe walls. Food residue, starch, crumbs, and non-flushable waste can then attach to that layer.

Animal fats may become firm as they cool, but liquid vegetable oils should not be treated as drain-safe. Their ability to remain liquid at room temperature does not stop them from coating plumbing or mixing with other FOG.

Cooking oil is therefore one part of a larger chain:

• Oil and grease enter pipes.

• Sticky residue develops.

• Food and household waste collect.

• Layers become thicker.

• Water flow becomes restricted.

One pan of oil does not automatically create a city fatberg. The larger concern is repeated disposal of oil and grease, which can help create the conditions for bigger blockages to develop over time.

Where Do Fatbergs Form?

The word fatberg is usually associated with large masses inside municipal sewer systems, but similar buildup can begin much closer to home.

Household Drains

A kitchen drain may develop a greasy coating that traps crumbs, starch, and food residue. This can cause slow drainage, unpleasant smells, gurgling, or a local clog.

Private Sewer Laterals

A sewer lateral carries wastewater from a property toward the public sewer. Grease and debris can collect in this line, particularly when flow is already restricted by pipe condition, roots, or structural defects.

Building Drain Lines

Apartments, restaurants, and shared buildings may have drain lines serving several kitchens or bathrooms. Improper disposal from multiple fixtures can contribute to buildup in a shared pipe.

Public Sewers

Larger fatbergs form when FOG combines with wipes and other materials inside public sewer infrastructure. These masses may interfere with normal wastewater movement and require removal by utility crews.

Why Fatbergs Matter to Homes and Communities

A fatberg matters because a sewer system needs open space to move wastewater safely. When grease and non-flushable waste reduce that space, wastewater may drain more slowly or stop moving altogether. A blockage can contribute to backups in homes, maintenance problems, and sanitary sewer overflows.

The EPA defines a sanitary sewer overflow as the release of untreated or partially treated sewage from a municipal sanitary sewer. It identifies FOG and some household products, including wipes marked as flushable, among the materials that may contribute to sewer problems.

Sewer overflows can affect homes, streets, public infrastructure, and water quality. The EPA notes that these releases may contaminate waterways and cause property damage when sewage backs up into buildings.

Keeping grease and wipes out of the sewer reduces preventable buildup and helps wastewater systems function as intended. For households, that is the most practical takeaway.

Common Fatberg Myths

Several everyday cleanup habits appear helpful but do not make grease safe for a drain.

“Hot Water Washes Grease Away”

Hot water may keep grease moving briefly, but the water cools as it travels through the plumbing. The grease may then settle or stick farther down the line.

Use warm water only after the visible oil and grease have been removed from the cookware.

“Dish Soap Dissolves Cooking Oil Completely”

Dish soap helps clean a light greasy film from plates and pans. It does not turn a visible pool of used oil into drain-safe wastewater.

Handle the oil first, then use dish soap to wash the remaining residue.

“A Small Amount Cannot Cause a Problem”

One small mistake may not create an immediate blockage. Repeated small amounts, however, can add to an existing greasy coating.

Seattle Public Utilities specifically addresses this myth and explains that small amounts can accumulate over time.

“The Garbage Disposal Handles Grease”

A garbage disposal breaks food into smaller particles. It does not remove grease from wastewater.

In fact, smaller food particles may stick more easily to grease already coating the pipe.

“The Toilet Is Safer Than the Sink”

Cooking oil and grease should not go into any household drain. This includes sinks, toilets, floor drains, utility sinks, and outdoor drains.

A stronger flush does not change how grease behaves inside the sewer system.

How Home Cooks Can Help Prevent Fatbergs

Fatberg prevention starts with deciding what to do with cooking oil before washing the pan. Visible oil should be kept out of drains. The right disposal method depends on the quantity, condition, and local waste rules.

How FryAway® Fits Into Oil Disposal

FryAway®  is one practical option for unwanted used cooking oil that is ready to be discarded. It is a disposal aid, not a drain cleaner and not a treatment for an existing fatberg.

The oil must be at least 170°F when FryAway is added. It should be hot, not warm or cooled. If the oil has fallen below 170°F, carefully reheat it to at least 170°F before adding FryAway. 

Follow three steps:

1. Sprinkle & Stir
   Confirm that the oil is still hot (at least 170°F). Turn off the heat, remove the food, add the correct amount of FryAway, and stir thoroughly. Turn off the heat, remove the food, add the correct amount of FryAway, and stir thoroughly. 

2. Cool
   Let the mixture cool and wait until solid.

3. Toss
   Lift out the tossable solid and place it in the trash according to local waste guidance.

Choose the product according to the oil quantity:

• Pan Fry Packets: Use one whole packet for 2 cups of oil.

• Super Fry: Use the included scoop when the quantity is smaller or varies.

• Multi Fry: Use for quantities ranging from a pan through to a turkey fryer.

• Deep Fry: Use one whole packet for 8 cups of oil, including oil in a deep fryer or Dutch oven.

Never divide a Pan Fry or Deep Fry packet. The packets are pre-portioned and should be used whole. For a detailed walkthrough, read how to solidify cooking oil.

Reuse Suitable Cooking Oil

If the oil is still fresh and suitable for another cooking session, allow it to cool completely before handling it. Filter out food particles, transfer the oil to a clean and dry container, label it, and store it away from heat and light. Oil that smells rancid, has become unusually dark or thick, foams excessively, or smokes earlier than expected should not be reused.

Filtering can remove crumbs, but it cannot restore oil that has already broken down. Reuse is a secondary option for oil that remains fresh and suitable for cooking. 

Use a Sealed Container

Cooled oil may be transferred into a secure disposable container when local trash rules allow.

Use a container that:

• Will not leak

• Has a secure lid

• Is stable when placed in the trash

• Can safely hold the cooled oil

Do not pour loose liquid oil directly into a trash bag.

Check Local Collection Options

Some communities accept used cooking oil at recycling or household-waste collection sites.

Before travelling to a facility, confirm:

• Whether cooking oil is accepted

• What type of container is required

• The maximum quantity

• Whether food particles must be removed

• The correct drop-off location

A collection site that accepts automotive oil may not accept cooking oil. For a broader comparison, read FryAway’s guide on how to dispose of cooking oil.

Scrape and Wipe Before Washing

Remove food scraps from plates and cookware before they reach the sink. For a thin greasy film, allow the cookware to cool and wipe it with a paper towel before washing. Use a sink strainer to catch crumbs and empty the strainer into the trash.

Keep Wipes Out of Toilets

Place wet wipes in a trash can, even when the package describes them as flushable. The same rule applies to cleaning wipes, facial wipes, paper towels, cotton products, and hygiene items.

A Simple Fatberg-Prevention Checklist

Use this checklist after cooking and during everyday cleanup:

• Keep used cooking oil out of every drain.

• Decide whether the oil will be discarded or reused.

• Use FryAway while the oil is still hot (at least 170°F) when solidifying unwanted oil. 

• Use whole pre-portioned packets as directed.

• Use Super Fry when the quantity requires an adjustable scoop.

• Allow container-bound oil to cool before transferring it.

• Scrape food from plates before washing.

• Wipe visible grease from cookware.

• Use a sink strainer for crumbs.

• Place all wipes in the trash.

• Check local rules for larger oil quantities.

• Contact a plumber when a drain repeatedly backs up or drains slowly.

Small Kitchen Habits Make a Real Difference

Fatbergs are not caused by one household or one cooking session. They develop when fats, oils, grease, wipes, and other unsuitable materials repeatedly enter connected drainage and sewer systems. That means prevention does not require a dramatic lifestyle change.

Handling visible cooking oil before washing the pan, keeping wipes out of toilets, scraping food into the trash, and following local disposal rules are all practical steps. These habits protect household plumbing while also reducing preventable material entering community sewer systems.

The goal is not to make home cooks feel guilty about frying. It is to make cleanup easier, clearer, and more responsible.

Frequently Asked Questions

What is a fatberg in simple terms?

A fatberg is a sewer blockage made from congealed fats, oils, and grease mixed with wipes and other materials that do not break down properly.

What causes fatbergs?

Fatbergs form when grease and oil enter sewers and combine with wet wipes, hygiene products, food debris, and other non-flushable waste. Repeated disposal allows the material to accumulate in layers.

How are fatbergs formed?

Grease enters a pipe, clings to surfaces, and traps solid material. Additional grease, wipes, and debris collect until the mass restricts wastewater flow.

Are fatbergs made only from cooking oil?

No. Cooking oil is one contributor. Fatbergs usually contain a combination of fats, oils, grease, wet wipes, personal care products, and other waste.

Can vegetable oil cause a fatberg?

Vegetable oil can contribute to fatberg formation because it may coat pipes, combine with other grease, and trap debris. It should not be poured into a sink, toilet, or other drain.

Does hot water stop grease from forming blockages?

No. Hot water may move grease temporarily, but it cools inside the plumbing. The grease can then stick or collect farther along the pipe.

Can fatbergs form in household pipes?

The term fatberg is usually used for larger public-sewer masses. Similar grease and debris buildup can form inside household drains and private sewer laterals, causing slow drainage or clogs.

How can home cooks help prevent fatbergs?

Keep cooking oil and grease out of drains, scrape plates, wipe greasy cookware, place wipes in the trash, and use an appropriate disposal method. When solidifying unwanted oil with FryAway, use it while the oil is still hot (at least 170°F). Sprinkle and stir, let the mixture cool until solid, and toss the tossable solid according to local guidance.