See the steps below and the full post here: http://www.hometalk.com/19246737/the-natural-drain-cleaner-for-your-clogged-drain
Step 1: Grab Vinegar, Baking Soda, and a Cup of Boiling Water
Step 2: Pour in Baking Soda
Step 3: Add Vinegar
Step 4: Once Drain Foams and Clears, Add Boiling Water