 Check for slow drainage or backups, and look for visible debris near the drain.  Pour boiling water down the drain to dissolve soap, grease, or fat, causing the blockage.  Firmly plunge the drain to create suction and dislodge the blockage.  Use a drain-cleaning wire or a coat hanger to remove clogs like hair or debris.  Place a bucket underneath, unscrew the U-bend, and clean out any residue.  Reattach the U-bend, ensure a watertight seal, and run water to confirm the blockage is cleared.