Thames Water said it was called out 101 times on Christmas Day 2010 to deal with blockages.
It said fat should be put in a container and, once it has cooled down, disposed of in a bin.
To highlight the problem a group of sewer men and women have posted on YouTube a rewritten version of the carol Deck the Halls
Thames Water said 25% more fat - about 500 tonnes - goes down drains in December than at any other time.
Rob Smith, Thames Water's chief sewer flusher and the Singing Sewermen's lead chorister, said: "Anything other than human waste and loo roll has no business in our sewers.
"And fat is the biggest no-no of all.
"Christmas time is the worst time of year for fat blocking our sewers because of all the turkey grease that gets washed away.
"It goes down sinks easily enough when it's warm but when it hits our sewers it cools down and sets hard forming hideous fatbergs."
This is the third year running that the Singing Sewermen have released a Christmas song, recorded in the sewers under the capital.
In 2009 they sung a reworking of God Rest Ye Merry Gentlemen and in 2010 they did their own version of Good King Wenceslas.
The video for this year's song was filmed in a Victorian brick sewer under east London.
People are being reminded not to pour fat from cooking Christmas dinners down the sink as it blocks up sewer pipes.