How To Plumb A Double Kitchen Sink With A Disposal And Dishwasher

We all hate dealing with food scraps, and having food clog up the kitchen sink is problematic for a number of reasons. With this in mind, many modern kitchens use garbage disposals. It is a straightforward process to install these appliances yourself and it will make dealing with dishes and food scraps easier than ever.

While the task may seem daunting, to install your garbage disposal and install a dishwasher with a double sink yourself is quite straightforward. You will need a couple of hours to do the installation and then the system will be ready to use. 

Introduction 

It can be a challenge for homeowners to connect up the appliances to a double kitchen sink themselves but this guide will walk you through the process step by step. Some double sinks already have the garbage disposal in their plumbing system which will reduce your installation work considerably. Others may already have a dishwasher drain connection. Different sinks have different features but no matter what your starting point is, it will be easy to install both appliances to your sink. As long as you have enough space under the sink to install everything it will be no problem at all with this task.  

Do You Need A Double Sink with a Dishwasher? 

Having a double sink is ideal for the purpose of food prep and stashing dirty dishes, it is a highly functional area. For best results, most homes decide to connect their double sink with a dishwasher and garbage disposal system. As a result, the area is made incredibly efficient and easy to use. A dishwasher is one of the key appliances in any kitchen, it makes cleaning the dishes easier, saves energy and saves you time. Fortunately, it is a simple process to install a dishwasher to a double sink. 

Are Garbage Disposals Worth It? 

There are a number of benefits to installing a garbage disposal. They help prevent clogging by dealing with the food that would otherwise go into the drainage system. Consequently, there is going to be a reduced need for repairs as the pipes are now protected from clogging. This can save you lots of money in plumbing repair costs. Garbage disposals are not only great for your home and drainage system but also help prevent your food scraps from going into the sewage and landfill. It’s a simple solution that helps homes manage their food waste better. 

How To Plumb a Double Kitchen Sink With Disposal and Dishwasher 

Follow these steps to install your garbage disposal and dishwasher to your double kitchen sink. Realistically, it’s going to take between 1 – 2 hours to connect everything up so take your time to ensure all of the connections are secure to avoid leaks. 

Plumbing Double Kitchen Sink with a Garbage Disposal (9 Easy Steps) 

Tools Required

• Voltage tester
• Pliers 
• Bucket 
• Cloth
• Screwdriver
• Hammer
• Plumber’s putty
• Putty knife

Step 1. Switch off the circuit breaker

First things first, you need to turn the power off at the circuit breaker so you can safely wire in the disposal. We like to be safe so use the voltage tester to check there is no electric current going to the wires before you start connecting wires. 

Step 2. Time to start work under the sink

With the power turned off, look under the sink and locate the couplers joining the drainage extension pipe and p-trap to the sink. Once you have located these couplers, use the pliers to remove them. Before removing anything it’s a good idea to position a bucket underneath the pipes so any water can be caught and disposed of. With the couplers removed, you can place a cloth in the drainage pipe to prevent bad smells from being released into the kitchen. 

Step 3. Separate the drain and sink

Next, remove the nut sitting below the coupling. The pliers can be used to do this and when the nut is loose you can separate the drain and the sink. 

Step 4. Remove old plumber’s putty 

When you remove the drain you will probably see some old plumber’s putty that is there from the initial installation. Use the gentle putty knife to remove this, it should be quite easy to clear. 

Step 5. Position the garbage disposal

In this step you will put the disposal unit in position. To start with, apply plumber’s putty around the edge of the disposal and then attach it to the flange in the sink. Position a mounting ring on the underside and use a screwdriver to secure it. Then wipe away any excess putty. As a result, the disposal should now be sitting securely next to the sink drain. 

Step 6. Connect the second sink drain 

After this, use silicone to seal the second drain’s sink flange and hold the tailpiece in place while you connect a tee. The tee is what allows you to attach the discharge unit to the disposal unit that is already installed in the first sink. This is for the purpose of both drains linking to the disposal unit rather than just one. 

Step 7. Attach the drain pipe

Now you need to attach the drain pipe to the bottom of the disposal. This allows water to flow through the disposal into the P-trap. If you are going to be installing a dishwasher, use a hammer and screwdriver to knock out the dishwasher drain block so you connect it. 

Step 8. Connect the electrics

Now both sinks are connected to the garbage disposal, you can connect the electrics. This is simply a case of removing the wire cover plate, matching the wires and connecting them. You can then neatly position the wires in the box and replace the cover. 

Step 9. Test

Lastly, you need to test the connection. This is so you can be sure that food waste will be caught in the disposal and both sinks are correctly connected to it. 

How to Install a Dishwasher to a Garbage Disposal 

Tools Required 

• Hose clamp
• Hammer
• Screwdriver
• Compression nut and washer

Step 1. Switch off the water

Firstly turn off the water supply. This is simply to make sure the system doesn’t leak while you are making adjustments to the plumbing. 

Step 2. Position the dishwasher drainage pipe

Next, install the drain pipe for the dishwasher. When doing this, make sure you include a high loop as this will help stop a backflow of dirty water from going back into the dishwasher. Importantly, some states require you install the dishwasher drain with an air gap so check if this is something you need to do. Either way it is a good idea to include these simple but effective preventative measures in your dishwasher installation.

It’s best to use a bracket or a clamp to keep the loop as high as you can underneath the sink. The idea is that the drainage pipe goes from a low position to a high position so water won’t flow backwards through the pipe. 

Step 3. Connect the drain pipe to the disposal 

Next you need to secure the dishwasher drain pipe to the inlet of the disposal. If you haven’t done so already, you will need to knock out the dishwasher drain blockers in the disposal system with a hammer and screwdriver. With the pipe now in position, clamp it using a hose clamp. You can also use a nut and washer if this came as part of your dishwasher’s installation kit. 

Step 4. Test

Finally, you can test the connection. As the dishwasher drainage is now connected you can turn the water back on. Turn the dishwasher on and put it on a test run so you can check it works without leaks. If there are leaks you will need to tighten the connections to prevent this from happening. 

How to Install a Dishwasher Drain to a Double Sink 

Things You Will Need

• Pliers
• Measuring tape
• PVC dishwasher wye tailpiece 
• Hacksaw
• 320-grit sandpaper 
• Washer

Step 1. Turn off the water

To begin with, turn off the water so you can make adjustments to the drainage system without worrying about accidents and leaks. 

Step 2. Locate the closest sink drain the dishwasher

Next, look under the sink and check which side is nearer to the dishwasher. When you install the dishwasher there is no point connecting the dishwasher drain to the furthest sink drain. From now on, make sure the remaining steps are applied to the closest drain.

Step 3. Loosen the drain slip nut

Look at the connection between the drain of the sink and the strainer basket to find the slip nut. This nut can be loosened with pliers until it can be moved along the tailpiece.

Step 4. Lift the tailpiece

With the slip nut now loosened you can lift the tailpiece. This is the piece that is connecting the double sink drains. After this, you can get rid of the slip nut that connected the basket and the tailpiece but leave the slip nut that is connecting the bottom of the tail.

Step 5. Measure the tailpiece

Measure the tailpiece length for the sink drain. Use this number to cut the dishwasher tailpiece so it will fit perfectly. You can cut the drain pipe using a saw and the edges can be smoothed using 320-grit sandpaper. 

Step 6. Replace the washer

Remove the slip nut’s old washer (this is what you didn’t remove earlier during step 4) and replace it with a new washer but leave the nut itself in place. 

Step 7. Secure the new wye tailpiece

After replacing the washer, use pliers to secure the new PVC dishwasher wye tailpiece. This is going to be secured into the slip nut on the drainage line.  

Step 8. Connect the wye tailpiece to the drain

Next, attach the other end of the tailpiece to the bottom of the basket. Connect the slip nut and the new washer, turning clockwise until it is secure. Pliers can be used to help tighten this securely. 

Step 9. Clamp the dishwasher drain line

Put a drain clamp hose onto the drain line. You now need to move the new drain line on top of the pipe that pokes out from the tailpiece you just installed. This is the part that was previously part of the sink’s drainage system. 

Step 10. Tighten and secure the system

Last but not least you can secure the pipe in position. Fasten the drain line for the dishwasher to the sink and tighten the clamp. You can now turn the water on and test the drainage system. 

Frequently Asked Questions 

It is more complicated to install garbage disposals and dishwashers to double sinks than it is to install them to a single sink. We’ve answered some common questions about this below. 

Can your garbage disposal affect your dishwasher? 

Yes, if the dishwasher drains through the disposal and the disposal becomes clogged or is draining slowly it will affect the dishwasher. You can continue to use the dishwasher if the disposal is broken but if it is clogged or not draining properly then it will need to be repaired so the dishwasher can drain as it should.

How expensive is it to install a garbage disposal? 

Installing a garbage disposal can cost between $100 – $600 depending on conditions such as the unit being installed and who is installing it. You can also install the disposal system yourself.  

Can the dishwasher and disposal be on the same circuit? 

Yes, they can be on the same circuit but the combined load must not exceed 80% of the circuit capacity. If you’re unsure, contact an electrician for advice on hardwiring or connecting them to your kitchen’s existing outlets. 

Conclusion 

A professional can charge hundreds of dollars to install a garbage disposal and dishwasher to your double kitchen sink but it is also something you can do yourself. The installation can be quick and easy depending on what is already installed in your double sinks plumbing system. Sometimes it is just a case of linking up the dishwasher or attaching the disposal rather than needing to install both from scratch. Whatever the situation, we have set out exactly how to do the installation in a simple step by step guide so you can get your kitchen sink fully functional in just a couple of hours.