Thames Water, the company that manages 43,500 miles of sewers under London, has a plea to Londoners this Christmas: please, please stop pouring cooking oil down the drain.

Dumping cooking fat down the kitchen sink leads to fatberg blockages, or giant blobs of congealed fat that stick to the top of pipes and prevent sewage from flowing. When the drains get blocked, all of that gunk can come back up through your toilet or sink. It’s disgusting.

Fatbergs are a persistent problem beneath London. In August, a team removed a Boeing-747 sized fatberg in Shepherd’s Bush Roads in West London. The summer before that, a 15-tonne lump of congealed fat clogged sewers in Kingston.

But the threat of fatbergs is even worse at Christmas when everyone is whipping up big, fat-filled feasts in their kitchens. All of that holiday cooking adds up to the equivalent of two extra Olympic-sized swimming pools of turkey fat that gets poured down the drain, according to the AFP.

“The fat situation is definitely getting worse. It’s building up in certain sewers it never did before,” Vincey Minney, a veteran worker at Thames Water, told the wire service.

Fatbergs form when the fatty acids in grease and oil bind with calcium found in the sewer. Wet wipes, cotton buds, and other non-flushable items cling to the fat, creating a hard, nasty mass. The congealed fat gets stuck to the ceilings of the pipes and becomes a problem as layers build up.

This year, the water authority released their own version of “The Twelve Days of Christmas” with reworded lyrics to discourage people from pouring fat down the sink. It’s part of the authority’s “Bin it, don’t block it” campaign.

Thames Water says that it deals with nearly 55,000 blockages each year at a cost of £12 million. Teams use high-pressure water jets to break up the fat, which gets flushed down the pipes and ends up in a landfill. It’s not a glamorous job. ”It’s about the nastiest stuff you can get. The diarrhoea stuff is a pleasure compared to this,” Minney told AFP. 

To prevent fatbergs, Thames Water says to collect cooking fat in an empty margarine tub or jam jar and throw it in the bin. Dinner plates should also be scraped before they are washed in the sink.

On that note, happy holidays!

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