DIY Guide: How To Plumb A Kitchen Sink With Garbage Disposal

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You might ask, “What is kitchen sink drain plumbing?” It’s simply the pipes and parts under your sink that take water away. “Can I plumb a kitchen sink with garbage disposal myself?” Yes, you likely can! It needs care and patience, but it’s a common DIY job. “How hard is it to plumb a kitchen sink with garbage disposal?” It’s not extremely difficult if you follow steps carefully. This guide will walk you through putting in or replacing kitchen sink drain plumbing that includes a garbage disposal.

How To Plumb A Kitchen Sink With Garbage Disposal
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Getting Ready for Work

Doing this job yourself can save money. It also gives you a good feeling of completing a project. Before you start, you need a plan. You also need the right tools and parts. Being ready makes the job go much easier.

You will deal with water and maybe old, dirty pipes. Wear old clothes you don’t mind getting messy. Have a bucket ready for water that will leak out.

What You Will Need

Here is a list of things you might need. Some parts might come with your new sink or disposal. Others you might need to buy. Check what you have before going to the store.

Tools:

Adjustable pliers or pipe wrench
Screwdriver (often Phillips head)
Hacksaw or PVC pipe cutter
Measuring tape
Safety glasses
Flashlight
Bucket
Rags or old towels
Level (small one is fine)

Materials:

New garbage disposal unit
New sink drain basket(s) (if replacing)
PVC or ABS drain pipes and fittings (these are usually white or black plastic)
Slip joint nuts and washers (often come with fittings, but good to have extras)
Drain tailpiece (often comes with sink basket)
Continuous waste tee (for double sinks)
Trap adapter
P-trap kit (kitchen sink drain trap)
Pipe thread sealant or Teflon tape (optional, but helpful)
Plumber’s putty (for the sink drain basket)

Safety First!

Working under the sink can be tricky. Here are some safety tips:

Turn off the power. Always, always turn off the power switch for the garbage disposal. This switch is often on the wall near the sink. If you can’t find it, turn off the power at your home’s main breaker box. Tape the switch off so nobody turns it on by accident.
Turn off the water. Find the hot and cold water valves under the sink. Turn them off tightly. If you can’t turn them by hand, use pliers gently. If your valves are old or leaky, this is a good time to replace them, but that’s a different project.
Wear safety glasses. Small pieces of old pipe or debris can fall. Protect your eyes.
Work in a well-lit area. Use a flashlight or work light so you can see what you are doing clearly.
Be careful with tools. Pliers can slip. Keep your hands safe.

Taking Out the Old Stuff

If you are putting in a new sink or replacing an old disposal, you need to take out the old drain pipes. This is often the messiest part.

Turning Off Power and Water (Again!)

Make sure the power to the disposal is off. Make sure the water valves under the sink are off. Open the sink faucet briefly to let out any water left in the pipes.

Getting Ready for Leaks

Put your bucket under the P-trap and the drain pipes. These pipes will have water in them. As you take them apart, water will spill out. Rags are helpful to wipe up spills.

Taking Apart the Old Pipes

Look at the pipes under your sink. You will see nuts holding the pipes together. These are called slip joint nuts.

Start at the P-trap. This is the curved pipe. Put your bucket under it.
Use your adjustable pliers to loosen the slip joint nuts on both sides of the P-trap. Turn the nuts to the left (counter-clockwise).
Once the nuts are loose, you can pull the P-trap away. Water will come out into your bucket.
Work your way up the drain pipes. Loosen the nuts holding the pipes to the sink drain basket and, if you have one, the old garbage disposal.
Take all the old drain pipes out.

Taking Out the Old Sink Drain Basket

If you are replacing the sink basket:

Under the sink, you should see a large nut holding the sink drain basket to the sink bottom. It might be plastic or metal.
Use large pliers or a basin wrench to hold the top part of the drain in the sink.
Use your adjustable pliers or basin wrench to turn the large nut under the sink to the left.
Once the nut is off, you can pull the drain basket out from the top of the sink.
Clean the sink drain opening well. Scrape away old plumber’s putty or sealant.

Putting in the Garbage Disposal

Now you are ready to start putting in the new parts. The garbage disposal installation is usually the first step under the sink.

Putting Together the Mounting Parts

Most disposals use a three-bolt mounting system. These parts connect the disposal to the sink drain hole.

Look at the parts that came with your disposal. You should have a rubber gasket, a fiber gasket, a support ring, a mounting ring, and a snap ring. There are also usually three bolts and a wrench tool.
From the top of the sink, push the rubber gasket into the drain opening.
From under the sink, push the fiber gasket onto the part of the gasket sticking down.
Next, put the support ring onto the gasket.
Then, put the mounting ring onto the support ring.
Push the snap ring into the groove on the mounting ring. You might need a flathead screwdriver to help push it in. This ring holds the whole assembly to the sink.

Connecting the Disposal Unit

Now you connect the heavy disposal unit to the mounting ring you just put in.

Make sure the rubber gasket inside the mounting ring is clean.
Lift the garbage disposal unit. It will have three “tabs” on the top neck that match the mounting ring.
Line up the tabs on the disposal with the openings on the mounting ring.
Push the disposal up firmly and twist it to the right (clockwise). The tabs should slide into place under the mounting ring.
Use the special wrench that came with the disposal. Put the wrench into the tabs on the disposal body. Twist the disposal unit firmly to the right until it is tight and feels locked into the mounting ring. It should hang safely from the sink.

Connecting the Electrical (Important!)

If you are not comfortable with electrical work, get help from an electrician.

Turn off the power at the breaker box! Double-check it is off.
Look on the bottom of the disposal unit. There should be a cover plate for the electrical wires. Take this plate off.
Inside, you will see wires. You will connect the wires from your home’s electrical cable (the one that goes to the disposal switch) to these wires.
Usually, you connect black wire to black wire, white wire to white wire, and green or bare copper wire (ground) to the green screw or wire.
Use wire nuts to make the connections tight and safe.
Put the cover plate back on the bottom of the disposal.
Make sure the electrical cable is safely held in place, often with a cable clamp where it enters the disposal body.

Assembling the Drain Pipes

Now you will start building the plumbing connections sink disposal setup. This is where you connect the disposal and the sink drain basket(s) to the wall drain pipe. This part involves putting together the sink drain assembly.

Understanding the Parts

The parts under your sink that connect the sink/disposal to the P-trap are often called the ‘branch drain’ or ‘fixture tailpiece assembly’. They are made of plastic pipes and fittings.

Tailpiece: A straight pipe that comes down from the sink drain basket or the top of the disposal outlet.
Continuous Waste Tee: Used in double sinks. This fitting connects the drain from one sink bowl to the pipe coming from the other bowl (or the disposal).
Baffles: Little plastic pieces that fit inside some fittings (like the continuous waste tee). They help direct water flow. Make sure you put these in correctly if your parts use them.

Connecting the Disposal Outlet

Your new garbage disposal will have an outlet pipe on its side. You need to connect a pipe from this outlet to the rest of your drain system.

Look at the disposal outlet. It usually has a rubber gasket and a metal flange.
Put the rubber gasket onto the disposal outlet.
Connect a piece of drain pipe to this outlet. This pipe is often 1 1/2 inches in diameter. It might be a special pipe that came with the disposal, or a standard drain pipe.
Slide a slip joint nut onto this pipe.
Push the pipe onto the disposal outlet, over the rubber gasket.
Tighten the slip joint nut onto the metal flange of the disposal outlet. Do this by hand first, then use pliers for about a quarter turn more. Don’t overtighten plastic nuts – they can break.

This is the start of your garbage disposal drain hookup.

Connecting the Sink Drain Basket (Single Sink)

If you have a single sink with a disposal, the pipe from the disposal outlet will connect to the P-trap. The sink drain basket itself doesn’t usually connect to the drain pipes in this setup, as the disposal takes care of draining the sink. The drain basket just connects to the disposal unit.

When you install the sink drain basket that goes into the garbage disposal:

Roll plumber’s putty into a rope shape.
Wrap the putty rope around the underside of the sink drain basket flange.
Push the drain basket down into the sink drain hole from the top. Press it down firmly.
Under the sink, wipe away any putty that squeezed out.
Follow the disposal instructions for connecting the bottom of the sink basket to the top of the disposal. This usually involves a fiber gasket and a nut that screws onto the bottom of the drain basket from inside the disposal collar area.

Connecting the Sink Drain Basket (Double Sink – No Disposal on This Side)

If you have a double sink and the disposal is only on one side, the other sink bowl will have a standard sink drain basket.

Put plumber’s putty under the lip of the sink drain basket.
Push the basket into the drain hole from the top.
Under the sink, put a rubber gasket, then a friction washer, then the large nut onto the bottom of the drain basket.
Tighten the large nut firmly by hand, then use pliers carefully.
Wipe away extra putty from the top of the sink.

Connecting Pipes for a Double Sink with Disposal

This is where you connect both sides of a double sink. One side goes to the disposal, the other goes to a standard drain. You use a continuous waste tee to join them. This is key for double sink plumbing with disposal.

The pipe from the standard sink drain basket (the side without the disposal) will connect horizontally towards the disposal side.
You will likely need a fitting called a ‘slip joint elbow’ or a straight pipe depending on the distance.
This pipe connects to one opening of the continuous waste tee.
The pipe from the garbage disposal outlet connects to the other opening of the continuous waste tee.
The single outlet on the continuous waste tee points downwards. This is where your P-trap will connect.

Make sure pipes slope slightly downwards towards the continuous waste tee and then towards the P-trap. This helps water flow away. A slight slope is usually enough.

Putting in the P-Trap

The P-trap is a very important part of your kitchen sink drain plumbing. It’s the curved pipe that holds a little bit of water all the time.

Deciphering the P-Trap’s Role

What does the P-trap do? That water in the curve acts like a seal. It stops bad smells and sewer gasses from coming up from the drain pipes into your kitchen. Without a P-trap, your kitchen would smell very bad. This is why the kitchen sink drain trap is required by building codes.

Parts of a P-Trap

A standard P-trap kit for kitchen sinks usually includes:

The curved trap piece (the ‘U’ bend)
A trap arm (a straight pipe piece)
Slip joint nuts and washers

Assembling and Installing the P-Trap

The P-trap connects to the pipe coming down from your sink/disposal setup and to the pipe coming out of the wall.

Look at the pipe coming down from your sink drain assembly or continuous waste tee.
Slide a slip joint nut and washer onto the end of the pipe coming down.
Take the curved P-trap piece. Put the open end onto the pipe coming down. Slide the nut down and tighten it onto the trap piece by hand.
Now look at the pipe coming out of your wall. This pipe usually has a fitting called a ‘trap adapter’ on the end. If it doesn’t, you might need to add one.
Take the P-trap arm (the straight piece). Slide a slip joint nut and washer onto one end.
Connect the end of the trap arm without the nut and washer into the trap adapter on the wall pipe. You might need to cut the trap arm to the right length using a hacksaw or PVC cutter.
Now, connect the other end of the trap arm (with the nut and washer) to the curved P-trap piece. You might need to turn the curved piece or the trap arm to line them up. Slide the nut down and tighten it onto the curved trap piece by hand.

Your P-trap installation is now mostly done. You should have a connection from your sink drain assembly or continuous waste tee, down into the curved P-trap, and then horizontally out the trap arm into the wall pipe.

Finishing the Plumbing

All the pieces are in place. Now you just need to make sure all the connections are tight and lined up correctly. This is the final step of plumbing connections sink disposal.

Connecting All the Pieces

You should now have a complete path for water:

From the sink drain basket(s) and/or disposal outlet.
Through tailpieces or disposal connections.
Through a continuous waste tee (if double sink).
Down into the P-trap.
From the P-trap arm into the wall drain pipe.

Make sure all the pipes are lined up well. They should connect straight into the fittings without being forced at an angle. Forcing pipes can cause leaks later.

Adjusting Pipe Lengths

You will likely need to cut some of the straight drain pipes to fit. Use your measuring tape to find the right length. Remember to account for how far the pipe pushes into the fitting. Cut the pipe using a hacksaw or PVC pipe cutter. Cut the pipe straight for the best fit.

Tightening Connections

Go back to every slip joint nut you connected.

Make sure the plastic washer (or rubber gasket) is sitting correctly inside the nut, against the pipe.
Tighten each nut by hand first. Make it as tight as you can comfortably by hand.
Use your adjustable pliers to give each nut a final tightening. Turn the nut about a quarter turn more. Do not overtighten, especially plastic nuts. This can crack them. Just make them snug.

Check the connections at the garbage disposal outlet, the sink drain basket(s), any continuous waste tee, the P-trap, and the connection to the wall pipe (trap adapter).

Your under kitchen sink drainage system is now connected.

Doing a Double Sink

Connecting a double sink with a disposal needs a few extra steps compared to a single sink. The goal is still the same: get water from both sink bowls and the disposal to one P-trap and then to the wall drain. This is the specific process for double sink plumbing with disposal.

How Double Sinks Are Different

With a double sink, you have two drain holes. One might have the garbage disposal unit attached directly under it. The other will have a standard sink drain basket. These two points need to meet before the water goes down the P-trap.

Adding a Continuous Waste Tee

The key part for double sinks is the continuous waste tee fitting. This fitting has three openings:

One opening points downwards, where the P-trap will attach.
Two openings are opposite each other horizontally. These are where the pipes from the two sink bowls connect.

Routing Pipes for Two Bowls

Disposal Side: A pipe comes out from the side outlet of the garbage disposal. This pipe will go horizontally towards the other sink bowl.
Non-Disposal Side: A pipe comes down from the sink drain basket on the side without the disposal (the tailpiece). This pipe might go straight down, then use an elbow fitting to turn horizontally towards the disposal side. Or, it might angle directly into the continuous waste tee depending on the setup.
Connecting to the Tee: Connect the horizontal pipe from the disposal and the horizontal pipe from the other sink basket into the side openings of the continuous waste tee. You will use slip joint nuts and washers for these connections.
Connecting the P-Trap: The outlet of the continuous waste tee points down. This is where you connect the top part of your P-trap.

Remember the slight slope for the horizontal pipes leading into the continuous waste tee. Water needs to flow easily from both sides into the main drain path.

This setup completes the garbage disposal drain hookup for a double sink.

Checking for Leaks

You’ve done all the work! Now it’s time to test your plumbing connections sink disposal. This is a very important step. Even a small leak can cause big problems over time.

How to Test Your Work

Make sure all slip joint nuts are snug (hand-tight plus about a quarter turn with pliers).
Make sure the garbage disposal mounting collar is tight.
Check the electrical connections (if you did them).
Turn the water valves back on under the sink.
Turn on the faucet to a low flow first. Check all the connections you made for any drips. Look at the disposal connections, all the slip joint nuts on the drain pipes, the P-trap, and the connection to the wall.
Let the water run for a minute or two. Look closely. Feel under the pipes with a dry rag or paper towel.
Fill the sink(s) partway with water. Let the water drain out all at once. This puts more pressure on the pipes and can show leaks that a slow flow might miss. Watch all connections as the water drains.
If you installed a disposal, make sure the power is back on. Briefly turn the disposal on to run some water through it. Listen and check connections near the disposal outlet.

Fixing Leaks

If you find a leak:

Turn off the water again.
Identify the leak. Where is it coming from? A nut? A fitting? The disposal itself?
Check the connection. Is the pipe seated correctly in the fitting? Is the washer in place?
Tighten the nut. Try tightening the slip joint nut just a little bit more. Don’t overtighten.
Take it apart and reassemble. If tightening doesn’t work, take the connection apart. Check the washer or gasket. Make sure the pipe end is clean and cut straight. Put it back together carefully, making sure the washer is seated right, and tighten the nut again.
Check for damage. Is the nut cracked? Is the pipe or fitting damaged? Replace any damaged parts.

Keep testing and fixing until there are no leaks, even when the sink is full and drains quickly.

Helpful Advice

Here are a few extra tips for your kitchen sink drain plumbing project.

Pipe Dope or Tape? Some people like to use pipe thread sealant (pipe dope) or Teflon tape on the threads of slip joint nuts. This can help make a better seal. Apply a little bit to the threads before tightening the nut. It’s not always needed with modern plastic washers, but it can add a layer of safety against leaks.
Dealing with Alignment: Sometimes, getting all the pipes to line up perfectly can be tricky. Plastic drain pipes and fittings offer some flexibility. You can often push or slightly bend the pipes to make the connections. Just don’t force them so much that they are under strain once connected. Cutting pipes to the exact right length is key here.
When to Call a Pro: If you run into problems you can’t solve, like a leak that won’t stop, or if the pipes coming out of your wall don’t match the standard sizes, it might be time to call a plumber. They have special tools and experience to fix tricky situations. Also, if you are not comfortable with the electrical part of the disposal installation, please call an electrician.

Keeping it Running Smoothly

Your new under kitchen sink drainage setup should work well for years if installed right. Here are some tips for maintenance:

Use the disposal correctly. Run water before, during, and after using the disposal. Grind small amounts at a time.
Know what not to grind. Avoid fibrous foods (celery, corn husks), pasta, rice (they expand), coffee grounds, grease, large bones, and non-food items. These can clog the pipes or damage the disposal.
Clean the drain regularly. Run cold water and a few ice cubes through the disposal occasionally. This helps clean the grinding chamber. You can also use citrus peels (lemon, lime) to freshen the drain.
Check for leaks now and then. While you are under the sink getting something, take a quick look at your drain pipes. Check for any wet spots or drips. Catching a small leak early can prevent bigger problems.

Frequently Asked Questions (FAQ)

Q: Can I use metal pipes instead of plastic (PVC/ABS)?

A: Yes, you can use metal drain pipes (like chrome-plated brass) for kitchen sinks. However, plastic is much more common now. It’s cheaper, easier to cut, and simple to join with slip joint fittings. If you mix metal and plastic parts, use a special ‘plastic to metal’ or ‘transition’ fitting if needed, though often slip joint fittings work fine as long as the sizes match.

Q: What size pipes do I need?

A: Kitchen sink drain plumbing usually uses 1 1/2 inch diameter pipes and fittings. Make sure all the pipes and fittings you buy are this size. The wall drain pipe might be larger (like 2 inches), but you will connect to it using a 1 1/2 inch trap adapter.

Q: Why is my drain slow after putting in the disposal?

A: A slow drain can mean a few things. It could be a partial clog somewhere in the new pipes or the wall drain. It could also mean the pipes are not sloped correctly, so water doesn’t flow downhill fast enough. Double-check your slopes. If you think it’s a clog, you might need to take apart the P-trap to clean it, or use a drain snake. Avoid chemical drain cleaners, especially with a disposal.

Q: Do I need a vent for my kitchen sink drain trap?

A: Yes, plumbing systems need venting. Vents let air into the drain pipes. This lets water flow smoothly and stops the water seal in the P-trap from being pulled out. Your sink’s drain is likely connected to your home’s main vent system in the walls. As long as the pipe you connect to in the wall is part of the main system, you don’t need to add a new vent just for the sink and disposal. However, if you are putting a sink in a new place far from existing plumbing, venting is a big deal and requires professional knowledge.

Q: What is plumber’s putty used for?

A: Plumber’s putty is a soft, moldable material used to make a watertight seal under the flange of sink drains, faucets, and other parts that sit on top of a fixture. You put it under the lip of the drain basket before putting it into the sink hole. When you tighten the nut underneath, the putty squeezes out, creating a seal between the metal flange and the sink surface.

Installing your own kitchen sink drain plumbing with a garbage disposal is a rewarding task. By taking your time, following these steps, and ensuring all connections are secure, you can successfully complete this DIY project.

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