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How to Install a Garbage Disposal

Garbage disposals are a helpful tool to help prevent pesky kitchen odors, as well as stop food from going down the pipes and causing plumbing issues. Watch as Ask This Old House plumbing and heating expert Richard Trethewey demonstrates how to install a garbage disposal in your kitchen.

In this video, Richard Trethewey teaches the process of installing a garbage disposal where there was not one originally.

What Is a Garbage Disposal For?

Garbage disposals are helpful to have because there’s less risk of plumbing drain damage from food going down the pipes, less trash being generated from food waste, and there is reduced kitchen odor from rotting food.

Steps for Installing a Garbage Disposal

People might want to try to install one themselves, so it’s important to understand the basics involved with the installation, particularly the parts and pieces that are needed.

It’s very easy to get confused in the plumbing aisle, so Richard breaks down the various PVC piping and fittings that can be found. These are the steps for how to install a garbage disposal.

  1. Disconnect the P-trap from the drain tail pipe with a wrench.
  2. Cut the P-trap near where it exits the cabinet, which is most likely from the side or the back of the cabinet, with a mini hacksaw. Keep a bucket underneath the P-trap for any waste or sludge that might have built up in the pipes.
  3. Disconnect the sink stopper and the tail pipe from the sink, which can be done from underneath with a wrench.
  4. Clean the old putty on the top of the sink.
  5. Apply plumber’s putty to the bottom of the new sink flange and place it in the drain hole.
  6. From underneath, secure the sink flange to the counter. Older models will use three screws that can be tightened with a screwdriver, and many models now use a plastic, hand-tightened ring.
  7. If the dishwasher hose needs to drain into the garbage disposal, most models come with a knockout hole that you can punch through to run the hose.
  8. Attach the disposal to the mounting ring that’s attached to the sink flange. It usually can twist right on and be hand tightened.
  9. Next, connect the P-trap. The hole for the drain line is usually on the side of the disposal, so new drain pipes will need to be run and connected.
  10. Seal all the connections for the new P-trap, depending on what type of piping is chosen.
  11. Open the faucet and check for any leaks.
  12. Plug the disposer into the outlet or call an electrician to wire the disposal to power.


What is a garbage disposal used for?

Garbage disposals are used to grind up pieces of food that go down the kitchen sink. They are helpful because there’s less risk of plumbing drain damage from food going down the pipes, less trash being generated from food waste, and reduced kitchen odor from rotting food.

What type of PVC pipe do I need?

You can purchase standard, Schedule 40 PVC pipes under your kitchen sink. You will need a P-trap, as well as fittings to connect it to the sewer line. You may want to purchase fittings of a few different angles to make sure that you can easily make the connection.

What is a P-trap?

A P-trap is a U-shaped piece of pipe underneath your sink. This will always retain a little bit of water, which prevents sewer gasses from rising up through the drain.


Richard installed a Badger 100 ⅓ Continuous Feed Garbage Disposal, which is manufactured by InSinkErator.

The other tools and materials he used to install the disposal, including the plumber’s putty, an array of PVC piping, fittings, cleaner, and glue and wrenches can all be found at home centers and plumbing supply houses.