When air gets trapped in your pipes around built-up debris, you may hear a gurgling sound when your sink is draining, and it may drain slowly. Clearing gunk from your drain does not always require chemicals or plumbing tools. Start by using everyday products. If that doesn't work, consider using specially formulated drain cleaners.
Bring a teakettle full of water to a boil on the stove. While it is heating up, wipe out your sink with a rag and pour 1/2 cup baking soda down your drain. If a sink stopper or strainer is in the way, push as much of the baking soda down the drain as you can with a cotton swab.
Pour 1/2 cup white vinegar down the drain after the baking soda and allow it to it fizz for a minute or two.
Pour the entire kettle of boiling water down the drain to rinse away the vinegar and baking soda.
Flush the drain with water from the tap for a few seconds to ensure the sink is draining more quickly and no longer gurgling. Repeat Steps 1 through 4 if water still drains slowly or if you still hear gurgling
Use an enzyme-based drain cleaner if you hear gurgling after the water has drained out of the sink indicating a build-up of grease in the pipes. Pour the enzymes down your drain before going to bed and allow them to break up the grease overnight. Flush the drain with tap water for a minute or two the next morning.
Plunge the drain with a small plunger if the sink continues to drain slowly or gurgle. This may loosen whatever is still getting in the way of draining the water but it can also worsen the problem by pushing debris farther down the drain.
Call a professional plumber if these problems continue.
Enzyme-based drain cleaners are more expensive than chemical-based cleaners but they are especially effective on grease.