Baking soda isn't just for baking; it is a powerhouse for cleaning for two main reasons:
Chemical drain cleaners (Drano, Liquid-Plumr, etc.) contain sodium hydroxide (lye) or sulfuric acid. Mixing them with vinegar or baking soda can cause:
Remove the cover and pour another 2 quarts of boiling (or very hot) water down the drain to flush away loosened debris and the resulting sodium acetate (a harmless salt).
Pour 1/2 cup of baking soda directly into the drain. Try to get it past the strainer and into the vertical pipe. Use a funnel if needed.
Pour 2 quarts of boiling water directly down the drain. This softens grease and loosens surface debris. Do not use boiling water if you have PVC pipes with glued joints that are old or compromised; use very hot tap water instead. (See safety section below).