Why a bathroom sink won’t drain could have many causes ranging from stuff dropped into the drain if there is no popup stopper in place, to a clogged line deep in the wall. A very common stoppage that is found is hair packed around the bathroom sink popup stopper and ball rod that activates the stopper. This is a simple problem that you should check before calling a plumber and it could save you hundreds of dollars that a plumber would charge unstopping a bathroom sink.
Some simple devices are sold that may be able to clean hair out of the bathroom sink popup area without taking anything apart like the Turbo Snake and Zip It which can be pushed down through the pop up area to catch the hair and pull it out. These will actually work in this application quite well.
What I would do is a little more complex but I feel it does a better job. I remove the popup and look down into the drain to see what is there and grab the hair out with a mechanics parts retriever tool sold in many places like Auto Zone or Advance Auto Parts for around $5. This tool is about 24” long and has a button that you push on one end that causes small metal fingers to open at the other end and when you release the button it will grab things with the metal fingers.
To get the popup stopper out on many bathroom sinks requires you to partially remove the ball rod to allow the popup stopper to unhook from the ball rod. The ball rod has a linkage attached to it that comes down from the faucet above and goes horizontally into the popup assembly below the sink. When you push and pull the button for the popup stopper on the faucet you will see this ball rod moving up and down at the rear, and pivoting at the end where it is connected to the pop up assembly. In most cases there is a nut that tightens this ball lever in place to the pop up assembly. You need to hold the popup, then unscrew this nut then pull the ball lever out about ½” to release the popup so it can be removed. Do not take the ball rod all the way out because on some there may be seals that you could lose, and once the popup is removed put the nut back on. Once the drain is cleaned you will want to run water to check the flow in the drain and if the ball rod is not in place and tight water will leak out under the sink.
With the bathroom sink popup stopper removed you have a clear view all the way down to the trap in most cases and the mechanics parts retriever can be used to remove anything that is clogging the drain all the way down to the trap. Lay a couple of paper towels on the sink to put the clumps of hair and stuff that you remove from the drain on and once you have it all removed wrap it up in the paper towel and throw it in the garbage. You are now ready to run water and see if you have fixed the problem. In many cases you will find that you have succeeded and saved a couple of hundred dollars for a plumber to clean your drain and will not have used any harsh or dangerous chemicals.
If you have succeeded in unclogging the bathroom sink, loosen the ball rod nut, and hold the popup stopper with the hole aligned properly to catch the ball rod. Slowly lower the popup straight down into the drain until it hits the ball rod, then pull the ball rod out slightly to allow the pop up to drop into place on the ball rod and reinsert the ball rod making sure the pop up is locked in on the ball rod and tighten the nut. Check the pop up stopper for operation and the ball rod for any signs of leakage.
Hopefully this has prevented needing a plumber to unclog your bathroom sink and saved you money. Any questions or, comments are welcome below.