The cold winter weather can cause any traces of grease, oil or fat inside your drains to harden, so pouring boiling or hot water down them can help remove any minor blockages before they become a larger, expensive problem.
There are lots of store-bought drain cleaning products that can be used, however they are often full of nasty chemicals and can do more harm than good. The best course of action is to contact a drainage expert who can carry out a jet blast of your drains to get them flowing properly. No chemicals needed!
Leslie Drain Clearing 