Turn off the faucet and remove any standing water from the sink
Put on gloves
Remove the sink stopper or drain strainer
Clear visible debris from the drain opening
Pour boiling water slowly down the drain
Add baking soda to the drain
Pour vinegar into the drain
Let the mixture sit for 10 to 15 minutes
Flush the drain with hot water
Use a plunger if the drain is still slow
Remove and clean the P-trap under the sink if needed
Scrub the drain pipe and trap with a bottle brush
Reassemble the pipes tightly
Run hot water to check flow
Repeat the cleaning if necessary