Double Kitchen Sink Plumbing: Complete Installation Guide

You’ve finally decided to turn practicality in your kitchen up a notch with a double kitchen sink. Congrats! The only issue is that plumbers charge sky-high fees. Since we live in the DIY era, it might have crossed your mind to do the plumbing yourself, but how?

Doing the plumbing for a double kitchen sink requires adding a drain assembly to the bottom of each sink before teeing them together. Things aren’t that different from a single sink setup but pay attention to assembling and sealing everything well to prevent leaks.

Introduction: Double Sink to One Drain

Installing a double kitchen sink can seem a bit of a nightmare, but the truth is you’ll only need basic plumbing skills. That is unless you want to throw a garbage disposal or dishwasher device into the equation – in which case you might be faced with a real nightmare if you don’t have solid plumbing knowledge. 

With that in mind, most homeowners embarking on kitchen sink plumbing projects only want to replace the standard sink with a double one for practical or design reasons.

Hoping you’ve modified the kitchen cabinet already to fit the bigger fixture, let’s find out how to fit the double sink to one drain.

Things You Will Need

  • PVC fittings with male threads and female slip ends
  • Pipe connectors 
  • Washers 
  • Channel locks
  • Teflon tape 
  • Kitchen drain trap kit
  • Plumber’s putty 
  • Sanitary tee
  • Kitchen sink strains with flange
  • Locknuts 
  • Pipe wrench
  • Screwdriver 
  • Pliers
  • Tape measure 
  • Hacksaw
  • Marker 

How to Install Double Kitchen Sink Plumbing (5 Easy Steps)

Once you’ve gathered all the necessary tools and materials, it’s time to start converting your single sink into a double. Don’t forget to turn off the water supply before starting.

Step 1 – Install the strainer and drain flange

The strainer and flange is the metal collar–strain combo placed at the bottom of the sink above the drain. Its role is to hold the pipes below the sink and prevent large chunks of food from being washed down the drain.

To install the flange and strainer, unscrew the locknut at the bottom of the strainer and remove both the locknut and the rubber washer. 

Knead a dollop of plumber’s putty into a roll and wrap it around the edge of the drain flange. Now, insert the strainer’s bottom into the drain hole and press it against the sink. From underneath the sink, tighten the locknut by hand until it grips, then use the pliers and continue tightening until you get an edge the size of a knife blade between the flange and the sink.

Step 2 – Attach the tailpiece and prepare your pipes 

The tailpiece connects the flange to the drainpipe and is very easy to install. This is a small section of pipe that extends from the bottom of the sink to the strainer, and all you have to do is to tighten it with pliers.

Repeat on the other sink, then grab the pipes and dry-fit the pieces together. Mark the spots where you need to cut, then use a hacksaw to cut appropriate sections of pipe for each of the sinks.

To decide the best drain configuration, check the placement of the wall drain. If the wall drain is in the middle of the two sinks, you should install a 90-degree elbow on each sink. If the wall drain is aligned with one of the sink drains, place a sanitary tee on the tailpiece nearest to the drain and a 90-degree elbow on the other tailpiece.

Step 3 – Install each sink drain

Install each sink drain by fitting the pipe onto the tailpiece. Secure it with channel locks and use Teflon tape to seal the pipe sections to the tailpieces.

If you have to install a longer section of pipe because the wall drain is aligned with one of the drains, make sure to maintain a slope of ¼ inch per foot of pipe. Otherwise, the pipe can clog easily, or you may experience drainage issues even if the pipes are clear.

Step 4 – Add the tee

If the wall drain is located between the two sink drains, grab a pipe tee and fit the end of each sink’s drain pipe into one end of the tee. Secure the sanitary tee to the drain pipes with compression nuts. Tighten them by hand first, then use a pair of pliers and secure the pipes as tight as you can.

To prevent leaks, you can insert compression washers into the junctions before assembling the pipes. As an extra anti-leak measure, seal each joint with Teflon tape.

If the wall drain is located near one sink drain, you can use a wye instead of a tee to connect the longer section of pipe to the other sink’s drain and the P-trap.

Step 5 – Install the P-trap 

Lastly, attach the longer section of the tee or wye to the upper section of the P-trap and secure it with compression nuts. Then, connect the P-trap to the wall drain and tighten all connections with channel locks. Only use light pressure to prevent damaging the pipes.  

Seal each joint with Teflon tape; then, you can proceed to attach the faucet to the sink. When you’re done, turn on the water and let it run for a few minutes. Make sure each sink drains properly and check for leaks. 

If you have drainage issues, it is likely you haven’t angled the pipes correctly, and you’ll have to redo the project. If in doubt, consider hiring an experienced plumber. 

Frequently Asked Questions

Hopefully, you now know the basics of plumbing a double kitchen sink, but you might still have some questions. We’re answering some of them below.

How Many P-Traps Does a Double Kitchen Sink Require?

A double sink only requires one P-trap. That’s because both sinks will drain water into the same wall drain, and each sink drain connects to the other through the tee. 

Installing two P-traps means trouble because the air may become trapped between the traps and lead to no drainage issues. For this reason, you should first connect the two sink drains together with a tee and then connect the tee to a single P-trap.

How Close to the Drain Does the P-Trap Need to Be?

Building codes don’t regulate the distance between the P-trap and the sink drain, but they regulate the maximum length of the tailpiece. According to the International Residential Code, the vertical distance between the tailpiece and the P-trap cannot be longer than 24 inches.

Any portion of horizontal plumbing must also have a slope of ¼ of an inch for every foot of pipe. Thus, the P-trap can be as close to the drain as you want, as long as it isn’t placed over 24 inches apart.

How Much Does a Double Kitchen Sink Cost?

Double kitchen sinks can cost anywhere from $65 to $6,000, depending on the material and design. Check the table below for the average double kitchen sink costs.

Double kitchen sink materialAverage price range
Stainless steel$200 - $550
Granite or composite $300 - $550
Porcelain or ceramic$750 - $1,200
Cast iron$800 - $1,350
Copper$1,000 - $2,000

Next Steps

Double kitchen sinks are elegant and practical. They can make your kitchen look more sophisticated while also providing you with more space to stash dishes or wash fruit and vegetables. Doing the plumbing for a double sink isn’t hard, so what now? Are you going to add a garbage disposal and dishwasher drain too? Tell us what you think and share your tips and secrets in a comment.

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