Does A Double Sink Vanity Share The Same Drain?

Does a double sink vanity share the same drain for both sinks? And does it need two traps below the sinks? We've done our research to find out the answers to these questions and more. 

A double sink vanity has two sinks. Each sink will need its own drain. But two sinks don't need their own p-traps. It is common practice for them to share one trap. Of course, you can have two if, for some reason, that works best for your application, but you'll just be spending money you don't necessarily need to spend.

We'll go into this in a bit more detail below and also answer a few of your other questions. Like can you replace a single vanity with a double sink vanity? And does your double sink need two p-traps?  What is a vent, and do you need it for your double vanity? We'll also talk about back-to-back sinks and if it's possible to install sinks that way. So please, keep reading.

Modern Double Sink in Bathroom. - Does A Double Sink Vanity Share The Same Drain? Fastening By Hand Copper Color Faucet To Marble Tile Wall In Bathroom.

Does A Double Sink Vanity Share The Same Drains Between Sinks?

Double sinks are such a joy if you have more than one person getting ready in the bathroom. It allows for space and makes sharing enjoyable. But what are the details of the plumbing for a double sink? We're going to break it down for you.

Interior of an ultra modern bathroom painted in white with a matching bathtub near the window

The Parts Of A Vanity

When thinking about your vanity, how exactly is it broken down? You have the cabinet or base with a vanity, which is the wooden part that either free floats on the wall or sits on the floor. It often has shelves or drawers for storage. The countertop is the piece that goes on top and is often made of granite or another hard material. Then you have your sinks, either one or two. And your fixtures which are the faucets to supply water and the handle or handles to turn it off.

Pre-made vanities often come with the base, the top, and the sinks altogether. Most don't come with the fixtures leaving that purchase up to the individual homeowner's taste. Click here for this double sink vanity on Amazon.

The Parts Of A Sink And The Sink's Plumbing

A stainless steel plumbing line of a sink inside a modern bathroom

The sink, our focus for this post, is the porcelain or composite basin that is waterproof and used for washing hands and brushing teeth. A sink is comprised of the basin and the drain. At the bottom of the sink is the hole where the drain pipe rests.

The drain attaches to a tailpipe which attaches to the PVC pipes that lead to the P-trap.  Other things under the sink are the water supply lines that supply water to the faucets and a cut-off valve that allows you to turn off the water to that unit without turning off the water to the whole house.

You can buy pop-up stopper sink drains individually, which is great if you found a sink basin without one. Many varieties and styles are available online. These are easy to install in your sink, and no extra tools are needed. Though, you will need to be able to attach it to your tailpipe. Click here for this on Amazon. 

Can You Replace A Single Vanity With A Double Sink?

Caucasian Handyman Worker Fastening By Hand Copper Color Faucet To Marble Tile Wall In Bathroom.

You can replace a single vanity with a double sink, but take these considerations into thought. First, consider the space available to have two sinks in your vanity, you'll need at least five feet of vanity length to comfortably have space for two. The ideal vanity size for two is at least six feet. If you don't have that space, you may have to reconfigure or give up something in the bathroom like a linen closet.

As for the plumbing, you may want to hire a professional to separate one drain into two. We found this handy video tutorial that gives a good overview of what is involved for a simple change from a single sink vanity to a double sink vanity.

Does A Double Sink Need Two P-traps?

Good news, your double sink doesn't need two P-straps. In fact, most plumbers will avoid this type of installation and use a T-configuration to lead both drains to one P-trap. There may be instances where your pipe coming in from the wall is too tall to work for one P-trap. In this instance, the plumber may opt for two.

A blue PVC trap with a series of waster lines in a commercial building

The P-trap is the bend in the PVC below your sink. It's shaped a bit like the letter 'P,' which is why it's called that. The bend in the pipe prevents gases from the sewer or the septic from backing up into your sink basin. 

How Close To The Drain Does The P-trap Need To Be?

As long as the P-trap is no further than 24" away from the drain, you can place it where you need to. But don't place it any further away from 24" away. If the attached trap arm running between the P-trap and vent pipe has a ¼” slope directed towards the drain, it doesn't matter how close the drain is to the P-trap itself.

Does Each Drain Need A Vent?

Drain pipe or sewer under kitchen sink. Pvc plastic pipe and flexible supply tube connection to stainless steel sink include faucet, trap for drain water and waste in drainage and plumbing system.

Every drain in your home requires a vent, even your bathroom sinks. These vents help prevent air locks from happening where the water might get stuck and then back up out of the pipe. If you've washed a bunch of smelly stuff, the last thing you want is that dirty water backing up into the sink. Typically though, most drains in your bathroom will lead to one master vent stack that goes through your walls and to the outside, typically through the roof of your home.

Can You Have Back-To-Back Sinks?

A back to back washing area

Back-to-back sinks can either be when two bathrooms share a wall, for a communal bathroom, or even in some master bathrooms when the designer and space dictate such a look. The plumbing specifics may be different for every area.

The first thing to figure out is if your drainpipe is large enough to handle the load from both sinks. Next, you'll need to figure out if each sink needs to have its own vent or if you can use one vent pipe for both sinks. Stacked tee fittings can be used, but then it may make one connection a lot lower than the other one.

Sink basins are not terribly expensive and can be found in a number of materials, from resin to porcelain. The main thing is that they are totally water and leakproof. Though basins can be as expensive as you want them, it's easy to find models for under a hundred dollars when you're building or remodeling. Click here for this one on Amazon.

Don't Rule Out Calling The Experts

Modern bathroom in luxury apartment.

If you want to be absolutely sure you're setting up your sinks correctly, hiring a plumber is always a good way to go. If they're licensed they're going to know the building codes for your area and make sure the work is up to snuff. You can do a lot of the demo on your own first, but don't skimp on the details. The last thing you'd want is an awkward installation or plumbing configuration that might cause problems down the road.

If you enjoyed this post here at, please check out a few of our others below:

How To Hide Pipes Behind A Bathroom Sink [7 Great Methods]

Why Does My Bathroom Sink Smell? [And What To Do About It]

A rustic designed vanity inside an earthy bathroom with a huge mirror, Does A Double Sink Vanity Share The Same Drain?

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