1/2 cup (150g) salt
1 cup (220g) baking soda
1 quart (1 liter) boiling water
When the kitchen sink is slow to drain, a sludgy build-up in the pipes may be the culprit. Let a trusted combination of salt and baking soda take the place of harsh chemicals that may be bad for the pipes. Pour the salt down the problem drain, followed by the baking soda. Let this mixture sit for several hours (overnight is best). Follow this up by pouring the boiling water down the drain to rinse it free of sediment.
Use every few months to prevent build up also