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Double Sink Plumbing: When and How It Is Done?

Many people like the convenience of having a double kitchen sink. They can wash dishes in one side and prepare food in the other at the same time. Although the sink size is doubled, they are still fairly easy items to install.

You just have to have the extra room. The problem comes in when you go to plumb them. Although there is still only one faucet, you still need to install two drain assemblies. It gets even more complicated if you have a dishwasher that uses the double sink drain lines too. In this article, I will talk a little more about double sink plumbing and how it’s done.

Be Precise When Doing Your Double Sink Drain line Plumbing

It definitely is tougher doing double kitchen sink plumbing than single sink plumbing even though they both only have a single drain. You have to add a drain assembly to the bottom of each sink before they ‘tee’ together to go down the single drain. That means you can run into more problems if you don’t do it right.

You also have twice as many problems you can run into with a double sink setup. So that means you have to be very careful that you plumb, so there is no restrictions or clogging. There are also twice as many places that can leak with a double sink drain setup.

How to Install Double Kitchen Sink Plumbing

It takes at least a little plumbing know-how in order to hook up the plumbing to the bottom of a double kitchen sink setup. With that said, it’s not something that is extremely difficult. So definitely don’t be intimidated before you start doing this project.

Remember, you are only dealing with one main drain and to somewhat short sink drain assemblies. Really the only thing that is different between a double and single sink setup is the two drain assemblies and the ‘tee’ fitting that connects them to the main drain.

Here are the main steps involved in plumbing the drain lines onto your double kitchen sink setup.

Step 1:

Once you have the sink in place, assemble all of the tools and other provisions, you will need to do the job.

We will be using PVC fittings that have male threaded and female slip ends on them. The female ends will also have a seal and pipe connector on them. There is no gluing involved in this project in most cases. You will need a pair of channel locks to tighten connections. You will also need Teflon tape to seal the threads on the pipe connections.

Step 2:

Next, I like to lay the parts out in front of me and kind of duplicate the way I feel they should go together under the sink. This lets me know I have all of the parts I need before I start the project.

Step 3:

Start by connecting an elbow with a long straight end onto one of the sink drain spouts. (On all pipe threads use a single wrap of Teflon tape to help make a good seal.) Do not tighten the connection all of the way.

Step 4:

Next, put the end of the pipe that is not connected onto the sink spout into one of the short ends of the ‘tee’ fitting. Again, do not tighten it all of the way.

Step 5:

Now, repeat steps 3 & 4 with the other side of the sink. You should then have both of the sink drain spouts plumbed into both short ends of the ‘tee’ fitting.

Step 6:

Attach the plumbing line trap to the longer bottom portion of the ‘tee’ fitting that has not been plumbed yet.

Step 7:

The final step is connecting the plumbing from the trap to the main drain line. Once this is done, tighten all of the connections with the channel. Only use light pressure, or you will break them.

Double Kitchen Sink Plumbing with Dishwasher

Some of you may be wondering how to plumb a dishwasher drain line into this setup. I often get asked if you need to add a third drain assembly into the mix. That’s not the case at all. It’s much simpler to set up a dishwasher drain line that.

Most likely, you have never seen water drain out of a dishwasher because their drain lines are usually hidden and fully enclosed. Dishwashers do not use as much water as you think. Because of that, they don’t need very large drain lines. Dishwasher drain lines don’t normally have to be any bigger than ¾”.

So, most plumbers simply use a ‘tee’ fitting cut into one of the two double sink drain lines to empty their wastewater into. It’s a very simple setup even if you are doing it as part of a retrofit. You must also be aware that if you have a garbage disposal, many times the manufacturer will include a connection that makes it simple to hook the dishwasher drain into it.

Josh Hurd

Bill Miller

Friday 9th of July 2021

What causes one side to backup into the other when draining?

Robert Robbins

Tuesday 23rd of November 2021

@Bill Miller, your main drain after the tee is plugged