In interior design, double sinks are becoming more popular than single sinks. The double feature is more visually pleasing and practical. The functionality of a double sink supersedes that of one sink, no questions asked.

Whether the sink is stainless steel, granite, composite, or ceramic, it suits most styles and makes the space look up-to-date. Double sinks are perfect for the kitchen and bathroom vanities.  

In the kitchen, they make cleaning dishes more efficient. Still, I’m sure people appreciate double sinks more in the bathroom, especially because there is less stress sharing the vanity (more so if you’re a couple).

Since we know how practical and efficient double sinks are, what’s their structure like?  

Do Double Sinks Need Two Traps?

Double sinks mean exactly that, two sinks. However, it does not mean that you need two traps. Each sink will need its own drain, but two traps are unnecessary.

Commonly, double sinks share a trap. However, you can choose to have two if it somehow works for your application (it’ll definitely cost you more).

Here’s what plumbers do. They use a T-configuration to lead the individual drains to one trap. One situation that I am sure of needing two traps is if the pipe coming from the wall is too tall.

In such a situation, a plumber opts for two.

Which Side of a Double Sink Should the Disposal Go?

More often than not, the double sink comes with two sinks of different sizes. One is smaller than the other and is also known as a veggie bowl.

With dishwashers, people don’t need to wash and rinse dishes manually anymore. All you need to do is scrape off the food leftovers and place the dishes in the dishwasher. Some people prefer to scrape, rinse and then place in the dishwasher.

Honestly, nothing is cast in stone with disposal placement. Many plumbers suggest placing the disposal in the smaller-sized sink. If you have double sinks of similar size, choose the one close to the dishwasher for disposal.

In my opinion, placing the disposal on the side that you scrape from most works best. Also, if you have a habit of piling dirty dishes on one side of the sink (most of us are guilty), place the disposal on that side.

You can always change the disposal placement if you feel it’s not working as you wish.

Where to Install Garbage Disposal in a Double Sink?

Firstly, the garbage disposal should go on one side. Normally, one sink drain (tailpipe) goes directly into the main drain pipe. The other sink drain (where the garbage disposal goes) is piped with a T into the main drain line.  

Ideally, the garbage disposal should go on the side that you do the scraping in. That aside, installing the garbage disposal on the shallow side places the device in a much higher position under the sink. Placing the garbage disposal on the shallower side leaves room for more clearance underneath.

The simplest way to ensure proper garbage disposal placement is to have the garbage disposal’s brand name facing the front. Manufacturers intend the disposal discharge to be in the back, going into its own trap.

From there, the waste line enters the mainline under the other sink’s drain line entry. Some plumbers suggest installing a separate trap and drain line for your disposal. However, what works for you might not work for the next person.

Get different opinions before settling on the best plumber for the job.

How Many P Traps are Needed for Double Sinks?

Before I give you any more information, a P-trap is a bend in the PVC below the sink. It’s called a P-trap because it is shaped like the letter ‘P.’ The bend prevents gases from backing up into your sink basin from the septic or sewer. 

P-traps are simply known as traps. As discussed above, double sinks do not need two traps unless they will function better this way.

There is a possibility of getting air pockets blocking the drain with two traps. If you insist on getting a trap for each sink, ensure the weir is of the correct size. Also, it is fine to have two traps if they are not double-trapped.

Does a Double Sink Need a Vent or Two Vents?

It is important to state that vents are absolutely necessary. Vents expel all the gases found in plumbing systems. Without them, drains would clog and cause foul smells all over the house.

Vents also bring in oxygen to the plumbing system to promote the easy breakdown of waste products. Before getting into the more complicated building laws and codes, a general rule of thumb in plumbing is that all drains need a trap, and all traps need a vent.

If you install two traps, you might need to install two vents. Before you get excited, check the building rules where you live and the codes to follow with such installations.

Pro Tip

The vent’s purpose is to allow air to come in, replacing the water as it drains out. While draining a double sink, ensure one side is closed while the other is open. It makes for faster drainage.

Can You Change a Double Sink to Single?

Switching from a double sink to a single sink is possible. However, it can get expensive. Getting a single sink to fit the dimensions you need might be difficult, especially after removing a double vanity.

You can get a custom sink made, but I am not certain if it is cheaper than buying a sink and countertop.

If you wonder if the previous connections can still work, the answer is yes. Pull the faucet off the old sink but keep the supply lines if they are still in good condition. 

Unfortunately, replacing a double vanity with a single sink gets tricky if more components, such as garbage disposal systems, are involved.   

It is advisable to hire a plumber to take care of the connections. This way, you avoid all the leaks and bursts that can come up with poor plumbing.

Are All Double Sinks the Same Size?

Double sinks come in different shapes and sizes. A standard double sink has a width of 22 inches, with some double sinks going up to 48 inches.

Additionally, one basin is not similar in size to the other. One kitchen sink basin is usually bigger for washing and the other for rinsing and scraping.

However, the sinks are of the same size in the bathroom because of “his” and “hers” functionality. You can choose sinks as wide or as deep as you wish. It all depends on preference and the brand you want to invest in.

Resources

Home Guides: How to Install Drain Lines for a Double Bowl Bathroom Sink

Home Décor Bliss: Does A Double Sink Vanity Share The Same Drain?

Common Size for a Double Bowl Kitchen Sink

Dry vent vs. wet vent