If water is backing up through the drain, it is an indication that there is a blockage somewhere in the plumbing system. This problem often occurs in the sink or bathroom where water is not able to flow freely through the pipes. Baking soda is a great natural cleaner that helps dissolve grease and oil in the drain. Simply sprinkle a cup of baking soda down the drain, then pour a cup of hot water over it and let it sit for a few minutes before flushing.