Boiling hot water, and a pipe snake.
What Is The Best Method Or Solution To Unblock A Bathroom Sink?
Generally and most simply start with drano that's what I do.. If that doesn't fix it then you need to try to "snake" it out.. Or call a plumber.
Coke, does it! Yep I use coke when I'm doing my daily chores and it works a treat. Once you use the coke make sure you rinse the sink immediately with hot water afterwards.