Workers from the Thames Water company in east London plead with customers not to pour grease down the drain, because it clogs the sewers. That message is sing the tune of "Good King Wenceslas". From the YouTube link:
Thames Water will donate 1p to WaterAid for every hit the film gets on YouTube (up to a maximum of 200,000 views, ending on 31 January 2011) to support the charity's life-saving work to improve access to safe water and sanitation to the world's poorest people.
Link -via Arbroath