One of the essentials of a modern kitchen is its garbage disposal unit. This unit shreds food waste into small enough pieces to flow through plumbing. On average, the unit can remain functional for up to twelve years. As such, the unit is essential to a functional kitchen and plumbing system.

Installing the unit for the first time requires intermediate to professional wiring and plumbing skills. For instance, most building codes require a 20-amp 120-volt outlet next to the unit. If you do not have an outlet under the sink, you will need to install one.

With these requirements, it is best to hire a professional with relevant experience on how to plumb a garbage disposal. Nonetheless, in this guide, we’ll show you all the steps involved in plumbing a garbage disposal.

Materials Needed to PLumb a Garbage Disposal

A garbage disposal unit is set up under your kitchen sink. To ensure optimal plumbing of the unit, you will need the following materials:

  • Tub of plumber’s putty.
  • Wire nuts.
  • Electrical tape.
  • Channel-type pliers or pipe wrench.
  • Flat-head and Phillips screwdriver.
  • Hacksaw or PVC cutter.

Steps Involved in Plumbing a Garbage Disposal

With all your materials in place, it is essential to read the instructions accompanying the garbage disposal unit. To make the process more convenient for you, we discuss the following steps on how to plumb a garbage disposal:

Dismantle The Existing System

Under your sink, you will find the existing drainage system. You need to dismantle this to plumb a garbage disposal unit. This step begins with disconnecting the p-trap pipe from the bottom of the sink. This is done using a pipe wrench or channel-lock pliers.

Set a bowl or towel to catch spills or leaks from the sink. With the p-trap pipe and the horizontal extension pipe dismantled, proceed to the large nut.


You will find this nut holding the strainer in place. Unscrew the nut using a wrench and remove the strainer body. Adjoined to the strainer body is the mounting assembly. Use a flat-head screwdriver to loosen the three screws on the mounting assembly.

After this, pry off the snap ring to complete the dismantling. Next, you prepare the new assembly. This preparation is essential to plumbing a garbage disposal.

Prepare New Assembly

With the former assembly dismantled, you will now prepare parts of the new assembly. You can begin by removing all the parts contained in the garbage disposal unit packaging.

Your new flange assembly is either pre-assembled or not. If it is, remove the snap ring that comes with it and other fasteners holding it in place.

Clean Out the Sink

The next thing is to clean your sink area to make plumbing your garbage disposal seamless. Here, you should focus your cleaning around the drain opening.

Apply Plumber’s Putty

To ensure water tightness and firmness, apply the plumber’s putty around the sink’s drain opening. Apply the putty to form a half-inch rope around the opening. You could use your fingers to smoothen the putty against the flange. Then, install the new sink flange into the drain opening and apply pressure against it.

For the best result, let the putty be visible around the flange. Find a weight to keep this pressure consistent and hold the flange in place. The weight could be the garbage disposal unit itself or a heavy jar. To avoid causing scratches to the sink or weight, place a towel between them.

Mount Sink’s Fastening System

The rest of the mounting happens from under the sink. Here, you’ll slide the fiber gasket, mounting flange, and backup flange over the sink flange. Hold these pieces in place with one hand. With your other hand, slip on the mounting and snap rings.

Use your flat-head screwdriver to tighten the three mounting screws around the ring. Alternate between screws in slow turns to achieve an even fit against the sink. You want the mounting assembly to be firmly fitted, not too tight. This will be helpful in case you need to make adjustments.

Prepare the Garbage Disposal Unit

Now, how to plumb a garbage disposal remains with the unit itself. Before mounting the garbage disposal, ensure you’ve already prepared the unit. The unit packaging contains a Romex connector, wire nuts, and a plug and cord.


In preparing the garbage disposal unit to function, there are two types of units you need to know about. These types come with two different kinds of preparation. One type of unit is the hardwired unit. To prepare this type of unit, you have to fit the wiring manually.

To manually connect the cord to the garbage disposal unit, follow these steps:

  • Turn over the garbage disposal unit to find its terminal cover plate at the bottom. Using a screwdriver, loosen the screws on the terminal cover plate. Remove every screw to gain access to the splice compartment. Remove only the cover plate and not the insulation shield from the splice compartment.
  • In the splice compartment, you will find black and white wires. Extend both wires so you can use them adequately.
  • Set the wire nuts on the Romex connector. Tighten each nut on the Romex connector until it lies against the connector’s shoulder. Identify the connector’s threaded barrel and screw it onto the lower-end frame.
  • Screw the barrel until it fits tightly against the lower-end frame.
  • On the Romex connector, you will find two screws. Loosen both screws and run the cord through the splice compartment. While doing that, ensure the Romex connector’s cord’s clamp encases the cord.
  • Once the clamp encases the cord on the outer insulation, tighten the two screws. Ensure the cord clamps tightly. You can do this with a strong pull to check whether the cord will slip or not.
  • Match the ribbed end of the white power cord to the extended white wire. Do the same for the extended black wire. Tighten the connected wires with wire nuts. Then wrap the connection using electrical tape.
  • Secure the green ground wire with the ring terminal in the splice compartment. Tighten the green ground screw.
  • Tuck all wire connections into the splice compartment. Cover the compartment with the terminal plate cover and screw firmly.

The other type of garbage disposal unit comes with the power cord factory fitted. To prepare this type of unit, simply check that the plug reaches its designated outlet.

Dishwasher Compatible Steps

With many modern kitchens comes a dishwasher. If this is a feature of your kitchen, the garbage disposal unit will be compatible with it. To learn how to plumb a garbage disposal with a dishwasher, follow the steps below:

Prepare Unit for Dishwasher Connection

To connect your dishwasher to your garbage disposal unit, locate the dishwasher inlet pipe. You will find this pipe near the top of the garbage disposal unit. Slowly put a screwdriver through this pipe. You will find a metal knockout plug blocking the pipe.

You will need to knock the metal plug out. You can use the screwdriver as a chisel with your hammer tapping against the metal. This process will have the metal plug out in no time.

Remove the metal particles from the pipe using pliers. Where the particles are so small, you could use your hands to remove them. Ensure that you remove all the metal particles.

Connect the Unit to the Dishwasher

On your dishwasher, you will find a drain hose. Slide a large clamp over the drain hose. Connect the drain hose to the dishwasher inlet pipe. Slide the clamp to the end of the drain hose and tighten it against the inlet.

For this connection, ensure there are no bends or folds. This will provide a steady flow of water. Also, ensure the connection is at least twenty inches above the kitchen floor. This distance will ensure drain water does not find its way back into the dishwasher.

Secure the Sink Connection to the Garbage Disposal

You may find the disposal unit heavy when securing it under the sink. To avoid straining yourself, find an object to prop up the unit. To secure the unit, align its top collar with the mounting assembly under the sink.

Raise the unit towards the assembly and rotate the top collar till the unit fits. You can tell the fitness of the unit when all the mounting tabs are locked in.

Connect the Discharge Tube

On the lower part of the garbage disposal unit, you will find an outlet. Slide a spring ring over the outlet and connect the discharge tube. Secure the tube with the spring ring.

Align Garbage Disposal Unit with Drainage Pipe

Rotate the garbage disposal unit to align its discharge tube with the drain trap. Connect the discharge tube to the drain trap. Secure this connection with a spring ring or nut.

If you find the discharge tube too long, cut off a necessary length. You can also purchase an extension if you find it too short.

Fasten the Unit

With the unit aligned with the sink’s three mounting tabs, screw the tabs firmly. Lock the unit into the assembly using a wrench. In securing the unit, ensure the collar snaps into place.

Run your tap and test the garbage disposal unit for leaks. Ensure there are no leaks from the discharge tube, the sink assembly, or the dishwasher. Now, turn on the socket to ensure it operates optimally.

Reach Out to Us Erica’s Plumbing in Boca Raton FL

Plumbing garbage disposal can be demanding especially if you have no prior experience. However, finding a dependable hand to attend to your demands should not be difficult. Call us today. We are happy to help.

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