Informational Guide

How To Properly Plumb A Double Sink

Everything you need to know about pipes and connections with a step-by-step guide on how to plumb a double kitchen sink quickly & easily.

by Ian Haynes

Double sinks are generally a lot larger than traditional sinks and give you a much larger workspace. Having two sinks can be a big advantage, and you’ll more people are now deciding that the best kitchen sink style for them is a double basin vanity.   

DIY plumbing is often a step too far for some people, but it’s a great way to save some money and get the satisfaction of installing something yourself. The size of a double sink vanity can make it even more intimidating, but it can certainly be done without professional help.  

This guide will explain everything you need to know about the pipes, connections, fittings and provide a step-by-step guide on how to plumb a vanity sink.  

rough-in is the step of the process where you’ve made all your holes in the wood, walls, floorboards etc., but you haven't yet connected up to your pipes. You should have measured everything, and this is your opportunity to make sure everything fits before securing it.  

For a sink, there's a couple of key measurements: 

  • Vertical Supply Lines
    There will be two holes for these usually. These should be 2-3 inches above the drain pipe for each sink. 
  • Horizontal Supply Lines
    These should be located 4 inches on either side of your drain pipe. 
  • Side To Side Buffer
    You should leave at least 15 inches around the side of the sink. 
  • Front Buffer
    Nothing should be installed less than 21 inches in front of the sink. 
  • Sink Drain Height
    Your kitchen sink should be at least 28 inches from the floor. For bathroom sinks, this is typically 24 inches. 
  • Vertical Discharge
    This should be 16-20 inches from the floor.

For double sinks sharing the same drain, you should make sure there is at least 30 inches between them. Where you have sinks of different heights, make sure that there’s no more than 6 inches difference.  

It’s imperative to measure and mark these points accurately during the rough-in, or you could face some serious issues with your plumbing. A full guide to doing this accurately is in the video below. 


How To Plumb Your Double Kitchen Sink  

Plumbing a kitchen sink can be intimidating, especially if you have a double basin. First, you need to get all your plumbing tools together, and then follow these steps:  

Plumbing A Double Kitchen Sink & Drain 

  • 1
    Turn Off Your Water Supply 
    This can be done by using your primary shut-off valve to stop the water supply to the whole house or by using your fixture shut-off valve to stop the water supply to the particular fitting. We’d recommend the fixture shut-off valve if you have one.  
  • 2
    Measure Up 
    Measure the distance between the shut-off valves and the faucets. This will determine how long your supply pipes need to be. 
  • 3
    Connect The Water Supply
    Install flexible piping to your faucets with a hot pipe and a cold pipe. The hot pipe should go to the left faucet and the cold to the right.  
  • 4
    Install The Tail Pieces
    Measure and cut two tail pieces. One should be installed underneath each sink and should be 2-3 inches long. Often with double basins, one will be deeper than the other; you should make sure the tailpieces extend to the same length, so you may need to trim one accordingly.  
  • 5
    Fit The J Pipes
    J- pipes will connect the tailpieces into the tee connectors, ultimately connecting the plumbing between the two sinks. Measure them accordingly and then fit a washer and nut to each tailpiece before sliding the J-pipe onto the end. You can then tighten the nut to secure it.  
  • 6
    Attach The Tee Connector
    Fit the Tee connector to the two J-pipes and attach using a washer and nuts.  
  • 7
    Connect The P-trap
    Slip a washer and nut over the end and connect the P-trap. This will be used to help stop any bad odor coming back up your pipes.  
  • 8
    Test The System
    Tighten all the nuts with a wrench and make sure they’re secure. Test the whole system by running water through the system and looking for leaks. The image below shows what it should look like. 
How To Plumb A Double Kitchen Sink

Plumbing A Double Kitchen Sink With Garbage Disposal 

Garbage disposals are a great way to break down food waste so it doesn’t clog up your plumbing. The garbage disposal will usually sit under just one sink, and all food waste should be directed into that one. To install a garbage disposal in a double sink, you need to: 

  • 1
    Disconnect All Electricals
    Make sure the garbage disposal is completely disconnected with no electricity running through it. 
  • 2
    Remove The Extension Pipe
    Remove the section of pipe between the sink and the P-trap. This is where your garbage extension will sit.  
  • 3
    Install The Garbage Disposal
    Attach the garbage disposal to the flange in the sink using plumbers putty around the edge. Use a mounting ring on the underside of the flange and snap it back to secure it in place. Use a screwdriver to secure the fitting.  
  • 4
    Attach To The Drain
    Attach the pipes to the bottom of the garbage disposal so that water can flow through it into the P-trap.  
  • 5
    Test The Connection
    The garbage disposal should now fit, so both sinks are flowing through it. Test the connection and make sure this is the case and that all food waste will be caught in the disposal.  
double sink plumbing

advantages of Double Kitchen Sinks

Double kitchen sinks aren’t a very new revelation, but they're becoming increasingly popular. There are a few key features that really set them apart from your traditional kitchen sink: 

  • Keeps The Clean Dishes Aside 
    We all know that surface space is at a premium in your kitchen. By having two sinks, you can keep your clean dishes in one to dry, removing the need for space-consuming drying racks where you’re trying to work.  
  • One Sink Is Specifically For Garbage Disposal 
    Garbage disposals are a great way to remove food waste from your kitchen safely. They literally churn up the bits of food until they’re small enough to pass through your plumbing without clogging it. A garbage disposal is often installed under one sink so that you can scrape food into it. This keeps your other sink free to be used as needed.  
  • Separate Soaking And Cleaning 
    If you have some tough stains on a pan, you need to let it soak, but having your sink completely occupied is frustrating and limits what you can do. Having two kitchen sinks allows you to continue using one sink while your pots and pans soak in the other, making your whole kitchen more efficient.  
  • More Multi-Tasking And Getting Things Done 
    Having two sinks just generally makes you more efficient. You can do more than one job, and you can have more than one person working at the sink. This ultimately makes life easier at home.  

Disadvantages of Double Kitchen Sinks 

As with any home purchase, you need to consider both sides of the equation. Double kitchen sinks aren’t for everyone, and there are a few things you need to consider: 

Consumes Large Counter Space 

Double kitchen sinks aren’t designed for compact kitchens. Double kitchen sinks can be over 48 inches long, which can really eat into your workspace. If you’re in an active kitchen, you may just decide that the workspace is more important.  

Eats Up Under-Counter Storage Space 

Similarly, double kitchen sinks can take up a lot of your storage space. Sink cabinets have no drawers or shelves and are generally just used for cleaning products. Having two of these means you’ve lost some valuable kitchen real estate.  

Less Space For Washing Large Items 

Some double kitchen sinks are actually more narrow or shallow than sink basins. This can make it more challenging to wash larger items like roasting dishes or baking trays.  

More Expensive 

You can find great value double and kitchen sinks, but on the whole, you'll pay more for a double sink. You should consider your budget before you commit to one or the other.  

double sinks

People also Ask (FAQs)

Does a double sink need two traps? 

No, it’s not a requirement to have two P-traps on a double sink because they will flow through the same drains. However, there is no issue in having two P-traps if they drain independently from each other. 

Can you connect two sinks to one drain? 

Yes, plumbing under the sink will connect two sinks, so they drain together.  

Can two sinks share a vent? 

Yes, but only where both sinks are the same level. If one sink is lower than the other, then the vent might not be at the right height to be effective.  

Can I swap a single-bowl for a double-bowl sink? 

Yes, providing you have enough space and the countertop materials are appropriate. You may need to make some minor adjustments to your kitchen, and you will need to plumb the double sink correctly.  

Compare single Vs double sinks here.

How much does it cost to install a double kitchen sink? 

The cost of your kitchen sink will vary massively depending on the make and model you go for. A good double kitchen sink can cost anywhere from $500-1500, and if you hire a professional, it will likely be another $300-500 on top of that. That money will obviously be saved if you install it yourself.  

Conclusion

Installing a double kitchen sink is a great way to make your kitchen more efficient. It can transform your kitchen into a more efficient workspace and allow you to carry out multiple jobs at once in the space. Plumbing a double sink vanity isn’t as difficult as it seems. It's all about taking it one step at a time.

Hopefully, this article has given you everything you need to get started and install the double vanity sink you've always wanted in your home.  

Ian Haynes is an expert writer who has successfully deployed over 500 plumbing pages and other related content. He has an excellent understanding of home plumbing issues and translates his experiences via Plumbing Lab so readers can have a better understanding of common household problems. Outside of his work, Ian likes exploring Brooklyn with his Labrador.

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