If your bathroom sink is slowly draining instead of holding water, your problem is super easy to fix. You likely just need to make a quick adjustment to the assembly under the sink. Pop-up drains have an arm that reaches down the drain and connects to a little rod. That rod sticks through the drain pipe and is held in place by a metal strip with holes in it. That strip, in turn, is connected to the little lever or handle you pull on to open and close the stopper. The video above from HomeAdditionPlus has an excellent look at how to make adjustments.
When a person has a blockage in their sewage system they often try to fix it themselves by adding an acid or a base such as Drano in an attempt to dissolve or dislodge the problem. These chemicals can get into the plumbers eyes when the sewage is splashed during the repair. The plumbers skin during the repair does come into contact with the sewage water. The owner of the toilet might not report to the plumber they have already tried Drano a highly caustic base .