STEP 1.Take a box of baking soda and pour ½ of it down the drain. Make sure not to combine this with any other chemical. You also want to do this dry. Do not water down the sink. Apply it as is down the drain in its powder form.
STEP 2. Next you want to take a ½ cup of vinegar and pour right after the baking soda. Be sure to have the washcloth or rag immediately ready to plug the hole in the sink. This needs to be done because the combination of the 2 substances will immediately cause an over flow of fizz, a chemical reaction similar to the eruption of a can of soda being opened after shaking it. You want the fizz to remain in the drain, not out.
STEP 3.Wait 30 minutes and boil some water, at least a ½ gallon.
STEP 4.Unplug the hole and slowly pour the boiling water down the drain. This method has been proven to be effective in pushing everything through the plumbing system. Letting the mixture sit longer will not remedy the problem any better. Vinegar is an ethanoic acid, and the baking soda acts as a base (sodium bicarbonate). When these two are combined, they will cause a fizzing reaction while forming carbon dioxide and a solution of the salt, sodium acetate.
Sometimes doing this experiment twice can be just as effective for good measure, but if it does not work and you still encounter a slow drain, make that call. Unless you are a true DIY kind of person, some repairs should be left to the experts. Be mindful of your limitations. Not doing it right the first time can be another expense you do not want to incur.