Can The Bathroom Sink And Bathtub Share A Drain? (THREE FACTORS)

Drains are an integral part of a functional bathroom.

They allow water and sewage to drain from your bathroom fixtures to the sewage system.

If you are modernizing your bathroom, you might be contemplating what fixtures can share the same drain.

So, Can The Bathroom Sink And Bathtub Share A Drain?

YES, your bathroom sink and bathtub can use the same drain as long as the drainpipe is well below the sink and shower level. For effectiveness, the drain pipe needs to be large enough to handle the combined water flow, and the two fixtures should be at most five feet apart.

If you are considering having your bathroom sink and bathtub connected to the same drain, there are several things to consider to ensure the systems work properly without gurgling.

Otherwise, you may have to deal with drainage issues.

This post will cover everything you need to know regarding connecting your bathroom sink and shower to the same drain.

Three Bathroom Sink And Bathtub Shared Drain Factors

While it is entirely possible for bathroom sinks and showers to share drains, it doesn’t work for every bathroom.

For this reason, it is imperative to determine whether your bathroom’s layout can allow for the setup.

For homeowners considering a combined drainage system for their sink and bathtub, here are considerations to determine whether you can have a common drainpipe for the two:

1. Bathroom Layout

For homeowners renovating their bathrooms and considering a shared drain for their sink and bathtub, you will need to determine whether your bathroom layout allows for the setup.

For instance, your sink and shower might be divided by a door or be far apart, making it impractical to connect the two fixtures to the same drainage system.

The idea is to determine whether the locations of your sink and shower allow for the improvements, which takes us to the next factor: spacing.

2. Spacing

The drain pipe of a shared bathtub and sink drainage system must be installed between the two fixtures.

As such, getting the spacing right will save you the stress of dealing with plumbing issues after installation.

Ideally, you want the two fixtures to be as close to each other as possible — not more than five feet apart.

That way, it will be easy to install a common vent in between and complete the plumbing to allow wastewater from the two fixtures to drain into one drainpipe.

3. Vent Placement

If your bathroom sink and bathtub are less than five feet apart, for the most part, it is possible to set up an arrangement such that they share a drain.

The only thing that can limit you is if your bathroom’s structural design doesn’t allow for a vent to be installed below the fixtures.

A vent allows fumes and odors to escape, while the shared drain lets wastewater flow to the treatment facility.

Three Pros Of Having A Shared Drain

Connecting your bathroom sink and bathtub to the same drain is economical because you will have one drainpipe to maintain.

If you are considering a shared drain, here are some benefits the setup offers.

1. Saves Space

To have a shared shower and sink drain, the two fixtures must be close to each other.

The arrangement also requires fewer pipes and ducts, which allows you to conserve space.

This makes shared drainage systems ideal for tiny bathrooms.

2. Shared Drains Are Cost-Effective

Installing a shared drain can help you save a lot of money.

Unlike when installing separate lines for each fixture, you will need a single pipe and one vent for a shared drainage system.

You will also save money on installation costs and maintenance costs.

3. Convenience

Installing only one drain pipe is more convenient.

If you run into plumbing issues, you will have an easier time detecting the issues, which makes maintenance of your drainage system easy.

Three Cons Of Having A Shared Drain

A shared drain must be installed properly to work best. Otherwise, you will have to deal with a host of plumbing issues and costly repairs.

Whether inadvertently or not, if a shared drainage system is not installed correctly, you will find yourself dealing with some of these issues, if not all.

1. Backflow

Connecting your bathroom sink and bathtub to the same drain often means streamlining your drainage system. However, sometimes it can mean creating a problem.

When a blockage occurs, it can result in the backflow of wastewater and, worse, bathroom flooding, which can be hazardous.

The sewage backflow will result in a bad smell in the bathroom and cause bacteria to spread.

Bathroom flooding can wreak havoc on your electrical appliances.

If you must install a shared drain, you can counter this potential issue by using a drainpipe that’s large enough to handle water and sewage from both fixtures.

2. Gurgling

Gurgling can be bothersome, and a shared drain is one of its common causes, particularly when it clogs.

With a clogged drain, the water flowing down displaces the drainage water, causing it to burp out, which produces glug glug sounds.

Having your drain inspected occasionally and unclogged can help solve this issue.

3. Slow Drains

When installing a shared drain, it is imperative to use a bigger drainpipe and vent.

Proper venting keeps sewage from getting trapped inside the pipes, especially the P-trap.

If the arrangement is not properly set up, it will likely result in slow drains, forcing you to use a plunger every time you shower.

With slower drains and poor venting, foul odors and sewer gasses will also be a problem.

For the most part, all these problems can be countered by proper installation.


Having your bathroom sink and bathtub share a drain is a great way to maximize space and efficiency.

However, this doesn’t mean every homeowner can install their sink and shower such that they drain to the same drainpipe.

Before setting up the arrangement, it is important to determine whether your bathroom design is fit for the arrangement.

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