Baking Soda and Boiling Water (vinegar if needed):
Feeling plugged up?
Pour 1/2 cup of baking soda into the problem drain, followed by 2 cups of boiling water.
If that isn’t doing it for you, chase the baking soda with a 1/2 cup of vinegar and cover tightly, allowing the vigorous fizzing of the chemical reaction to break up the gunk.
Then flush that with one gallon of boiling water.