Remove the sink stopper or drain cover
Pour boiling water into the drain (if the pipes are metal)
Use a plunger to create suction and force
Mix baking soda and vinegar, pour into the drain, let sit 30–60 minutes, then flush with hot water
Use a drain snake/auger to reach and break up clogs
Remove the P-trap:
Place a bucket under the P-trap
Loosen slip nuts on both ends
Clear debris from the trap and drain line
Reinstall the P-trap and tighten securely
Check for clogs in the overflow opening (if applicable) and clear with a small tool
If the clog remains, call a plumber and request drain line hydro-jetting or camera inspection