Clean trap or plug. You will notice that there may be residue of hairs and soap accumulated under the trap or the plug that is inside or over the drain. Remove the screws that fix the trap and to remove the cap you will have to turn it and lift it. Rub any dirt or hair that has accumulated.
Boil water in a boiling jar. Fill it up with water, as there is no exact measurement to use. Bring the water to a boil. You can use a large saucepan to boil if you do not have a kettle.
Pour the water directly into the drain. This could cause it to uncover immediately. Remember that you should not splash the boiling water because it could burn you. Then pour it into the bathtub to verify that it functions normally.
Pour 1/4 cup of baking soda and 1 cup of white vinegar into the drain. If pouring hot water did not unlatter it, use baking soda and vinegar to remove excess dirt.
Wait 15 to 20 minutes. Let the baking soda and vinegar stand between 15 and 20 minutes. You can use a stopwatch to control the time.
Boil more water in the boiling jar. Once again, fill it with water and bring it to a boil.
Pour the hot water directly into the drain. The water will react with the baking soda and vinegar, and will uncover the drainage. Try the bathtub to see if this method unlocked and try another if it was not. The baking soda and vinegar mixture does not use chemicals and usually works for mild cases, so it will not always work.