. Before cleaning it out, make sure you have not used a drain-clearing product, because they contain chemicals that are irritating to the skin. Place a large bowl or bucket at the foot of the sink, so as to collect the water and debris that will come out of the drain; and put on a pair of strong rubber gloves.
Follow the pipe below the drain until you find a ring; unscrew it firmly but without ruining it, and if you find a lot of resistance find a wrench, which will allow you to exert more force on the ring. Unscrew it completely and then remove the pipe from the discharge and let its contents fall into the bucket prepared for the purpose.
With your fingers check that the drain and the tube are clean, and if necessary remove anything that is still preventing discharge. Put the tube back into position and reposition the nut, tightening it firmly.