How to Unclog A Drain With Baking Soda and Vinegar
Pour a pot of boiling hot water down your drain,, about 2 quarts.
Dump in about 1/2 c. baking soda. Let that sit for a few minutes.
Then, pour a mixture of 1 c. vinegar and 1. c very hot water down on top of the baking soda.
Cover with a drain plug (to keep the reaction down below the drain surface) if you have one and let it sit for 5-10 minutes.
Flush one more time with a pot of boiling water.

I used to use this all the time after my first clogged drain necessitated a plumber call.