Unclogging a drain is a process that normally requires using homemade or commercial drain cleaners, but commercial drain cleaners are known for damaging the pipe itself. Depending on the severity of the blockage, you need vinegar, salt and baking soda to make homemade drain cleaner. For harsher blockages, a plunger or auger is needed.
Pour 1/2 cup of baking soda down the drain and another 1/2 cup of vinegar. The fusion of these chemicals can create fumes, so it's important to be careful. Allow it to settle for 3 hours and then run water through the drain. As an alternative, you can try adding 1/2 cup of baking soda and 1/2 cup of salt to the drain and leaving it in overnight.
Fill the clogged basin with water to cover the head portion of the plunger. Before applying the plunger, you can use petroleum jelly on the suction lips to attain better suction. Exert up and down strokes until the water flushes down. Repeat as many times as necessary.
A drain-and-trap auger is very effective for unclogging drains. Remove the stopper and feed in the snake. Crank the handle and adjust the thumbscrew as necessary. Keep turning the handle of the auger if you meet resistance in the drain. Continue moving the handle while withdrawing the auger.