Mix 1/2 cup baking soda with 1/4 cup table salt and pour down the drain giving you trouble. Follow by pouring 1 cup of heated vinegar down the drain (it will foam and bubble).

Cover the drain with a plug or duct tape to prevent the mixture from escaping. Let it sit for 15 minutes. After 15 minutes, run hot tap water or pour boiling water down the drain for 30-60 seconds.