How to Replace a Garbage Disposal and Install a Standard Sink Drain

Begin by ensuring the work area is safe and prepared. Turn off the dedicated circuit breaker for the garbage disposal in your home's main electrical panel. As a secondary precaution, unplug the disposal's power cord from the outlet under the sink. Clear out all items from the cabinet under the sink to give yourself ample room to work. Place a bucket directly under the P-trap and disposal drain outlet to catch any residual water. Lay down several old towels to absorb any spills and protect the cabinet floor. Wear your safety glasses to protect your eyes from debris and water drips.

With the bucket in position, locate the dishwasher drain hose, which is typically a flexible, ribbed hose connected to a side inlet on the garbage disposal. Use a flathead screwdriver or pliers to loosen the hose clamp and carefully pull the hose off the disposal's inlet port. Tuck the hose upward to prevent water from siphoning out. Next, identify the large slip nuts connecting the P-trap assembly to the disposal's discharge pipe and the main drain line in the wall. Using channel-lock pliers, turn these nuts counter-clockwise to loosen and disconnect the P-trap. Some water will drain out, so be ready with your bucket.

Garbage disposals are heavy. Support the unit from below with one hand or prop it up on a stack of books or a block of wood. Locate the mounting ring at the very top of the disposal where it connects to the sink flange. Insert the tip of your disposal wrench (or a large flathead screwdriver) into one of the lugs on the lower mounting ring. Turn the ring counter-clockwise about a quarter-turn until it disengages from the ramps on the upper mounting ring. The disposal will drop slightly. Carefully lower the heavy unit and remove it from the cabinet.

From underneath the sink, use a screwdriver to loosen the three screws on the mounting assembly. Once loose, use a flathead screwdriver to pry off the metal snap ring that holds the assembly together. Be careful as the ring can be under tension. With the snap ring removed, all parts of the mounting assembly (mounting ring, backup flange) will come off. From inside the sink bowl, push the old sink flange up and out from underneath. Use a putty knife to scrape away all the old, hardened plumber's putty from the sink's drain opening. Clean the area thoroughly with a rag and cleaner to ensure a good seal for the new drain.

Take a generous amount of plumber's putty and roll it between your palms to form a rope about 1/2-inch thick and long enough to circle the drain opening. Apply this rope of putty to the underside of the new sink strainer's flange. From the top of the sink, press the new strainer firmly into the clean drain opening. You should see an even ring of putty squeeze out around the edge. From underneath the sink, slide the rubber gasket, followed by the fiber friction washer, and then the large metal locknut over the strainer's body. Hand-tighten the locknut as much as possible. To fully tighten, insert the handles of your channel-lock pliers or a screwdriver into the lugs on the locknut and turn clockwise while holding the strainer basket steady from above to prevent it from spinning. Tighten until the assembly is snug and secure. Use a putty knife or your finger to remove the excess putty that squeezed out inside the sink bowl.

Now you will assemble the new drain pipes. First, attach the new flanged tailpiece to the bottom of the sink strainer you just installed, securing it with the provided slip nut and washer. For the double-basin sink, you will use a 'continuous waste' or 'branch' tailpiece that has a side inlet. Connect this to the drain on the other sink basin. Connect the dishwasher drain hose to the side inlet port on this branch tailpiece and secure it with the hose clamp. Make sure to create a 'high loop' with the dishwasher hose by securing it as high as possible under the countertop before it connects to the tailpiece; this prevents dirty water from flowing back into the dishwasher. Finally, connect the P-trap to the bottom of the new tailpiece assembly and to the drain pipe in the wall. You may need to dry-fit and cut some of the PVC pipes to the correct length using a tubing cutter or hacksaw. Hand-tighten all slip nuts, then give a final quarter-turn with channel-lock pliers.

The final step is to check your work for leaks. Place a dry towel or paper towel under the entire drain assembly. Turn on the cold water and let it run for a minute, carefully checking every joint and connection point for drips. Then, turn on the hot water and repeat the process, as heat can sometimes expose a loose connection. For a thorough test, close the sink stoppers and fill both sink basins about halfway with water. Then, release the stoppers simultaneously to send a large volume of water through the new plumbing. Inspect carefully for any leaks. If you find a leak, it is likely at a slip nut connection; try tightening it another quarter-turn. Once you are confident there are no leaks, turn the circuit breaker back on. Clean up your tools, remove the bucket and towels, and return items to the cabinet.