The illegal practice nets millions of dollars every year. 

By Elisabeth Sherman
Updated August 17, 2017
Andres Ruffo / EyeEm / Getty Images

Monstrous so-called "fatbergs" made of grease and garbage are floating through sewers across the globe, blocking and breaking pipes, clogging toilets, and generally wreaking havoc. It probably doesn’t really sound like something you’d want to find in your kitchen, but some people are now illegally harvesting the globs of fat to make cooking oil.

National Geographic reports that these fatbergs begin to coalesce when someone in the aboveground world dumps grease down the kitchen sink, then another person down the street flushes their dirty paper towels, while someone else throws their bacon grease straight out of the pan and into the drain, all of which collects and congeals below. If these blobs get big enough, they block sewer systems, sending raw sewage gushing out onto the streets. A 15-ton fatberg was pulled from a London sewer in 2013, while New York City has spent $18 million dollars in the past five years trying to fight these floating disasters.

In many places, including the United States, where grease traps are required in restaurants, thieves have broken in and stolen the accumulated grease to convert to cooking oil, which they then sell on the black market for a hefty return. An estimated $75 million worth of cooking oil is stolen in the U.S. every year. The same thing happens in China, where enterprising criminals steal fat from sewers and grease traps, clean it up only minimally, and then sell the resulting “gutter oil” on the black market. In the U.K., where fatbergs are a growing nuisance, sewer workers have now been specifically tasked with the unpleasant job of cleaning out the fat-filled pipes and drains around the Thames themselves.

Scientists have now taken on how to efficiently dispose of the fatbergs. Some are developing sensors that would alert cities to the presence of these blobs before they can cause serious damage, while others are considering ways to make fuel out of the fat.

Want to be sure that you aren’t contributing to the fatberg epidemic? National Geographic points out that so-called flushable wet wipes are a huge part of the problem. You can also read our handy guide to substances you should most definitely not pour down your drain here.