Before starting any work, prepare your workspace. Put on safety goggles to protect your eyes from splashes and rubber gloves to keep your hands clean and protected. Clear out everything from the cabinet under the kitchen sink to give yourself ample room to work. Place an empty bucket directly beneath the U-shaped pipe (the P-trap) to catch any water or debris that will spill during the process.

Bring a large pot or kettle of water to a rolling boil. Carefully carry the boiling water to the sink and slowly pour it directly down the clogged drain. If you have a double sink, pour it down the side with the garbage disposal. Pour the water in two or three stages, waiting a minute between each pour. The intense heat can sometimes be enough to melt the solidified grease, allowing it to be flushed down the pipe.

If boiling water doesn't work, try a natural chemical reaction. First, remove as much standing water from the sink as possible. Pour about one cup of baking soda directly into the drain opening. Follow this with one cup of white vinegar. The mixture will immediately begin to fizz and bubble. Place a drain stopper or a wet rag over the drain opening to contain the reaction and direct its force downwards into the clog. Let it sit for 15-30 minutes. Finally, flush the drain with another large pot of boiling water.

If the drain is still clogged, use a cup plunger. For a double sink, you must seal the other drain opening completely. Use a wet rag or a drain stopper to plug the non-clogged side. If you have a garbage disposal, plunge that side. Run a few inches of water into the sink to allow the plunger to form a seal. Place the cup plunger over the drain and press down firmly to create a tight seal. Vigorously pump the plunger up and down for about 30 seconds. Pull the plunger off quickly to break the seal. The alternating pressure and suction can dislodge the clog.

If plunging fails, the clog is likely in the P-trap. With your bucket positioned underneath, use a pair of channel-lock pliers to loosen the two large slip nuts holding the curved P-trap in place. You may be able to loosen them by hand. Once loose, unscrew them the rest of the way and gently pull the trap downwards. Be ready for water and sludge to spill into the bucket. Take the P-trap to another sink or outside, empty its contents, and use a bottle brush or a bent wire coat hanger to scrub out all the grease and debris. Rinse it thoroughly, then reinstall it, making sure any washers are properly seated. Hand-tighten the nuts first, then give them a final quarter-turn with the pliers.

If the P-trap was clear, the blockage is further down the line. With the P-trap removed, insert the end of a drain snake (or auger) into the drainpipe that goes into the wall (the trap arm). Push the snake into the pipe until you feel resistance. Lock the cable in place and slowly turn the crank clockwise. This rotational motion will either break up the clog or allow the corkscrew tip to grab onto it. Continue to push forward and rotate. If you grab the clog, pull the snake back out slowly, cleaning the cable with a rag as you go. Repeat until the pipe is clear.

Once you believe the clog is cleared, reattach the P-trap if you removed it. Ensure the slip nuts are snug but not over-tightened. Remove all tools and the bucket from the sink basin and cabinet. Turn on the hot water tap and let it run at full pressure for several minutes. This will flush out any remaining grease or debris from the line. While the water is running, carefully inspect all the pipe connections you worked on, especially the P-trap slip nuts, to check for any drips or leaks. Dry the connections with a rag and check again to be sure.