Vinegar and baking soda clean drains because they react to each other when they are mixed. Baking soda is a bicarbonate, and vinegar is an acetic acid.
The reaction of vinegar and baking soda combined causes them to bubble quickly. The bubbles move through the drain, cleaning dirt and debris from the walls of the drain. After pouring the baking soda down the drain, pour in the vinegar. Allow the mixture to react and bubble for approximately five minutes.
Flush the drain with approximately 2 quarts of boiling water. The boiling water continues to push the mixture down the drain.