Blockage in Trap - How to Unclog a Drain - Bob Vila
Check the Trap
If the drain is still clogged, you may have a blockage in the trap, which is the curved section of pipe underneath the sink. Place a bucket under the trap and then unscrew it using pliers or a pipe wrench. Typically, just unscrewing the trap will dislodge any clog; you can also poke a flexible piece of plastic tubing into the pipe to loosen any material clinging to the sides.