Use a Plunger to Unclog Sink
The easiest way to unclog a sink drain is to use a plunger. Fill the sink with about 4 inches of water. If the clogged drain is in the kitchen with twin basins, fill both sides with about 4 inches of water.
Either get someone to help or with a free hand hold a rag over the disposer drain. Rapidly plunge the drain in the other sink about a dozen times. If the drain is still clogged, switch sinks and plunge the other side to unclog the sink.
Boiling Water to Unclog Sink
In kitchen sinks, pouring boiling water down the drain can sometimes help unclog the sink. Be sure to use caution when handling boiling water.
Slowly pour the boiling water down the drain to help dislodge any greasy buildup or debris that might have lodged in the opening of the drain. After pouring the boiling water in the drain you can try plunging again to remove any additional blockage.
Remove the Trap to Unclog Sink
If the drain remains clogged after plunging you will need to remove the trap underneath. Place a large bucket or catch pan underneath the trap to catch the water that will run out of the sink. Loosen and remove the slip nuts on either end of the trap. Be sure to keep one hand on the trap to keep it from popping off unexpectedly.
If the clog is in the trap or the pipe leading from the sink, clean it out and reassemble the trap.
If you do not see the clog in the trap or the pipe leading from the sink you will need to use an auger in the pipe going into the wall. Carefully work the auger into the pipe to remove the clog.
Once you believe the clog has been removed, reassemble the trap and test the sink.
You might also be interested in how to unclog a tub.