Pour 1/4 to 1/2 cup of baking soda directly into the drain.
Hair clogs.
Wet/dry shop vacuum (best) OR a heavy-duty trash bag. Procedure (with shop vac): how to unblock bathroom sink without plunger
Boil a full kettle of water. Pour it slowly down the drain in two or three stages, allowing the hot water to work for several seconds between each pour. Pour 1/4 to 1/2 cup of baking soda directly into the drain