Slow water drainage can be caused by a build-up of grease, hair or soap in the U-bend under the sink. If the pipe isn’t totally blocked, try a homemade drain cleaner of half a cup of bi-carb soda, a cup of white vinegar and four litres of boiling water. Pour down the drain and repeat if necessary. It should take care of any greasy build-up, but solid blockages need to be removed using these steps. –
Dismantle the U-bend - If the sink remains blocked, place a bucket under the U-bend. Wrap masking tape around the nuts on both sides of the U-bend and loosen with a pair of large multigrips. Remove the U-bend and pour excess water into the bucket. - See more at: http://www.readersdigest.com.au/how-to-unblock-ubends#sthash.hbU5PwY6.dpuf