If your kitchen sink backs up and you have a garbage disposal, it's a good bet that something is caught in the disposal. If you clear it and the drain is still blocked, you may be tempted to pour some heavy-duty drain cleaner in the disposal. Resist that temptation -- it might do more harm than good. Rely instead on chemical-free drain-cleaning standbys -- a plunger, a snake and adjustable pliers. If you really like chemicals, choose ones that won't eat through your pipes and give you skin burns.
If the drain is stopped up completely, clearing the disposal should get water flowing again, but grease and fibers that have collected in the pipes will keep it flowing slowly. You have to clear the pipes, but the presence of the disposal complicates the procedure somewhat.
Step 1 Clear the disposal.
Check the breaker to make sure it hasn't tripped. With the disposal switched off, turn the disposal rotor back and forth using the key that came with it -- or use a 1/4-inch hex wrench. The wrench fits into a slot underneath the disposal canister. If you need to retrieve anything from the disposal, do it with tongs -- never your hands. Once the rotor is turning freely, press the red reset button and turn on the disposal to drain standing water.
Step 2 Plunge the sink.
Secure the dishwasher drain hose to the tailpiece with a clamp to prevent it from blowing off, and cover overflow holes in the sink with duct tape. If the sink is empty, run the water until there's about an inch in the bottom of the sink. Fit a sink plunger around the garbage disposal opening and pump vigorously several times. Let water drain, then plunge more, if necessary. If the drain is still blocked, clean out the P-trap and waste pipe.
Step 3 Clean the P-trap.
Release the clamp holding the dishwasher drain hose, but leave the hose connected. Unscrew the P-trap from beside the garbage disposal, using adjustable pliers if you can't do it by hand, and swing it away. Unscrew the other end of the trap from the waste arm, take the trap outside and clean it with a garden hose. Pull fibers from the garbage disposal outlet.
Step 4 Snake the waste pipe.
Before replacing the P-trap, feed a drain auger -- or snake -- into the waste arm, push it as far as it will go and crank the handle to work the head through blockages and obstructions within. If you prefer the chemical drain-cleaner approach, this is the best time to use one. Pour a citric or phosphoric acid-based commercial cleaner into the waste opening, or use vinegar and baking soda. If you choose the vinegar/baking soda approach, mix 1/2 cup of baking soda with 1 cup of vinegar and squirt it into the pipes with a turkey baster. Wait for 10 to 20 minutes, then use the baster to flush the pipes with some hot water.
Step 5 Maintain the drain.
Avoid pouring grease down the drain, and refrain from grinding celery, corn husks or other fibrous materials. Keep the garbage disposal clear by periodically grinding a mixture of ice, salt and a few lemon or orange peels.