blocked pipe?

Look under the sink and you'll either find a bottle trap or a 'U' bend which will be filled with grot. The bottle trap bottom simply unscrews, likewise the 'U' trap which needs dismantling fully to clean it. Both jobs simple but rather unpleasant! You could try a chemical unblocker I guess - something like Mr. Muscle plug and sink cleaner. Never used it though - probably works in ideal conditions.

John
April 2008