Back in 2017, a team of workers in London put on hazmat suits, climbed into an old sewer under a busy street, and started attacking a giant lump with high-pressure hoses. It looked like a wall of dirty rock. They kept at it, seven days a week, for three weeks. Matt Rimmer from Thames Water, the man in charge, told reporters it was “basically like trying to break up concrete.”
It wasn’t rock. It was 130 tons (about 118 tonnes) of hardened cooking fat and household junk, the length of two football fields. And it hadn’t come from a factory. It came from ordinary kitchens, one greasy pan at a time.
In December 2025, Thames Water found another one in the same spot. A 100-ton (roughly 91 tonnes) “grandchild,” built the same way.
If you cooked bacon this week and rinsed the pan under hot water, or drained the fat off a pound of ground beef into the sink and cranked the tap to chase it, you already do the thing that builds those. Almost every American home does. And even after decades of plumbers begging people to stop, most of us still don’t know what actually happens inside the pipe.
The habit that seems completely fine
Ask ten neighbors what to do with a pan of hot bacon fat. Most will tell you the same thing your parents probably told you: pour it down the sink, run the hot water hard, add a squirt of dish soap, done.
It looks like it works, too. The pan comes clean. The water goes down. You wipe the counter and move on.
Water utilities across the country have spent years trying to get homeowners to stop doing this exact routine. Iowa State University Extension puts it bluntly: drains hit with oil and grease will clog over time, even if you only pour a few drops in the sink.
A few drops. From a habit that feels harmless. So what’s actually going on down there?
The 47% number nobody talks about
Before we get to the how, look at the scale. The U.S. Environmental Protection Agency (EPA) put out a report to Congress on sewer overflows and found that grease is the number one cause of sewer blockages in America, responsible for 47% of them. Not roots. Not wipes. Not diapers. Grease.
The same report estimates the country sees between 23,000 and 75,000 sanitary sewer overflows every year, and that doesn’t count sewage that backs up inside homes. A big chunk of those trace back to what people are pouring down their kitchen sinks.
The London fatberg is just the version big enough to make the news. The one under your street, or under your own kitchen floor, is quietly forming right now. And it isn’t only bacon grease doing it.
It isn’t the food. It isn’t the soap. It isn’t even the temperature of the water. The reason the “just pour and rinse” habit fails has almost nothing to do with what you’re pouring, and almost everything to do with what happens to it about three feet after you can’t see it anymore.
What’s really happening inside the pipe
Here it is in plain terms.
When you pour hot grease down the drain, it goes in as a liquid. But it only stays a liquid for a few feet. The pipe under your kitchen floor isn’t warm. It sits at whatever temperature your floor or wall happens to be, usually 60 to 75°F (about 16 to 24°C). Bacon fat and other animal fats start turning solid again at around 95 to 115°F (35 to 46°C). So within a few feet of the drain, the grease cools off, gets sticky, and starts clinging to the inside of the pipe.
Running hot water after it doesn’t help. It just pushes the melted grease a little farther down before the same thing happens. Hockers Plumbing spells it out: hot water only keeps grease liquid for a moment, and it hardens up again farther down the pipe. Dish soap doesn’t save you either. In the drain, it’s a squirt of soap against cups of fat. The soap dilutes and washes away. The grease stays.
And here’s the twist most people never hear. It isn’t just solid stuff like bacon fat or lard. Olive oil, vegetable oil, and canola oil do the exact same thing. They stay liquid on your counter, sure, but once they’re inside a cool pipe they still coat the walls, still catch food scraps, and still add to the clog. Mr. Rooter’s plumbing team says it plainly: cooking oils that are liquid at room temperature should never go down the drain either.
Now picture what’s actually building up. Every time you rinse a greasy pan, a thin waxy film gets left behind inside the pipe. It doesn’t wash off with the next load of dishes, because water and oil don’t mix. The next rinse leaves another layer. And another. The layer grabs onto passing food bits, coffee grounds, and eggshell pieces, and glues them into itself. The pipe gets narrower. Water drains slower. By the time your sink is gurgling, the coating has usually been building for months or years.
If that sounds like your kitchen, you’re the rule, not the exception. And the fix is almost embarrassingly simple.
The fix that keeps drains clear for years
The EPA, Iowa State Extension, Clemson University’s Home and Garden Information Center, and water utilities across the country all give the same three-word rule: cool it, can it, trash it. Here is what that looks like at your sink.
- Don’t pour any hot fat or oil down the drain. Not bacon grease, not burger drippings, not leftover frying oil, not olive oil from a marinade, not the fat off ground beef. If it came out of a pan and it’s fatty, it doesn’t go in the sink.
- Pour it into something you can throw away. An old tin can, a glass jar, or a foil-lined mug all work. Let it cool on the counter until it turns solid, then drop the whole thing in the trash. Cook fatty meals a lot? Keep a dedicated jar under the sink and add to it until it fills up.
- Wipe greasy pans with a dry paper towel before you wash them. This is the single most important step for oils that never fully harden, like olive oil. A quick wipe pulls almost all the fat off the pan and into the trash. Clemson Extension recommends this move directly.
- Skip the garbage disposal for anything fatty. It only chops food scraps, it does nothing to stop grease from going down the drain.
- If you deep-fry, save the used oil in a sealed jug. Check if your city has a cooking oil drop-off (many do). If not, seal the jug tight and trash it.
No products to buy. No tools. A jar and a paper towel.
What you save
Getting a plumber to clear a grease-clogged drain isn’t cheap. Hydro-jetting, the pressure-hose method plumbers use on stubborn kitchen clogs, runs $350 to $600 (about €320 to €550, or £280 to £480) for a standard job, and can push past $1,000 (roughly €920 or £800) if the buildup is bad, according to HomeAdvisor’s national pricing data. That’s the cost of a 30-second habit skipped enough times.
The workers who eventually pulled the London fatberg out had to dry a piece of it for weeks before it was safe to touch. That is where household grease ends up. Not gone. Just sitting there, waiting.
Sources: (1) London Museum, The Whitechapel Fatberg; (2) NPR, Behold The Fatberg: London’s 130-Ton, ‘Rock-Solid’ Sewer Blockage; (3) Thames Water, 100-tonne Whitechapel fatberg discovered; (4) Hockers Plumbing, Can You Pour Grease Down the Drain With Hot Water?; (5) U.S. EPA, Controlling Fats, Oils, and Grease Discharges from Food Service Establishments; (6) U.S. EPA, Sanitary Sewer Overflows; (7) Iowa State University Extension and Outreach, Proper Disposal of Fats, Oils, and Grease; (8) Clemson University HGIC, F.O.G. Pollution; (9) Mr. Rooter, Why You Should Never Pour Grease Down the Drain; (10) HomeAdvisor, How Much Does Hydro Jetting Cost?.
