A slow, sluggish sink drain is a very common plumbing problem. The bathroom sink is the one most frequently afflicted with this particular problem, and several things can contribute to a slow sink drain. Often the pop-up that is used to stop up the sink can collect a lot of hair and debris, because the sink is used on a daily basis.
Also, soap and other products that are washed down the drain can slowly collect in the drain pipes. The build-up that naturally collects over time reduces the size of the drain, effectively slowing the progress of draining water. This drainage issue happens naturally over time and usually cannot be avoided. The only solution is to clean the drain periodically to keep it flowing.
There are several ways to address a drainage problem, as outlined here.
Source: The Spruce
