Garbage Disposal Plumbing

A garbage disposal.
  • 2 hours
  • Intermediate
  • 50-200
What You'll Need
Outlet T or Y fitting
Plumbers putty or Teflon tape
Garbage disposal

A badly done garbage disposal plumbing job leaves you with the risk of clogging your drainage system and causing all kinds of plumbing problems. If you have never installed a garbage disposal unit before, you should either call a professional or research thoroughly how to undertake the project.

Step 1 - Understand Schematics

Installing a waste disposal unit requires careful consideration. Be sure to understand how your current set up works. If you have a double sink set up in your kitchen you will need to remove the drain pipes from the sink you choose to adopt the garbage disposal unit. Double sinks are double drained and the feed pipe, which goes from one sink to the waste pipe, will have to be disconnected and removed. Underneath the sink, be sure to turn off the stop valves for both hot and cold water. They should have isolator valves coming from each of the faucets.

Step 2 - Start Plumbing

Once the isolator valves have shut the water off, undo the small tailpiece from the sink which will have the garbage disposal installed. That is the part directly under the drainage hole. Loosen the tailpiece and then trace along to the next point of connection. This could either be a longer tailpiece or an outlet T. In some cases, it could be a Y-fitting, so if it is, undo the tailpiece that connects the two sinks and remove it.

Step 3 - Attach Garbage Disposal

Attach the garbage disposal unit with any parts that were supplied with it. After that you will need to make sure the exit pipe is facing the other sink, so line it up correctly before you completely tighten it. If it is running directly across at A level, measure a straight piece of pipe. If it goes into the wall behind the other sink at an A angle, turn the garbage disposal to face that in a straight line, then tighten it.

You'll need to cut a new tailpiece to fit between the garbage disposal and the opposing sink. Make sure you measure it exactly and cut the piece long enough that you can screw on the other tailpieces to attach both ends. You will also need to be precise about the P-trap that runs from the drainage. Remember that at this point you will need two adaptors if you are using a Y-fitting.

Step 4 - Secure

Both the garbage disposal and the sink need to drain into the main drainage system, which is usually a pipe out to the exterior wall. Secure all the fittings with plumbers putty or Teflon tape. Once you have secured them and they are tightened and lined up, you can proceed to turn the isolator valves back into the ‘on’ position. The water will then start to flow back through the system and you can turn on the waste disposal and make sure everything runs ok.