Can a Toilet and Sink Share the Same Drain? (Explained!)

After learning that the toilet and the kitchen sink use the same water, it’s easy to conclude that they both drain at the same place. So, can a toilet and sink share the same drain?

The answer is Yes; a toilet and sink can share the same drain if, for one, the toilet pipe is large enough to hold the combined flow, and two, the two pipes form a perfect fit, and you use a common valve within a 1.5m radius.   

Overall, the toilet pipe must be large enough to contain the combined flow (toilet and sink wastewater) to avoid the water bursting off and causing leakage.   

Also, should you install a common vent to prevent airlock that causes wastewater backflow. But as for the 1.5m radius, it’s usually a building regulation that you have to adhere to.

Let me explain more!

can a tub and sink share the same drain

How The Toilet and The Sink Use the Same Drain

Generally, all drains of your house empty their contents at a commonplace known as the sewer. That includes the toilet and the sink drain. In turn, the sewer collects all wastewater and transports everything to the local sewage treatment plant.

Note, however, that the sewer may be a distance away from your home, and that could force your building contractors or expert plumbers to resort to combining the toilet, and the sink drains just within your compound.

Considering that the toilet drain is larger than the sink drain, the expert will install a common vent that makes it easy for the sink water to drain into the larger toilet vent without risking an airlock.

Airlock could cause a wastewater backflow, something you should avoid at all costs.

How to Safely Combine the Toilet and Sink Drain

Overall, the key to having the toilet and sink share the same drain is ensuring you install them properly. In that case, here are the priority areas:

  • The larger drain (the toilet pipe)

Generally, the larger drain should be larger enough to hold the combined floor. And when speaking of the larger drain, I’m talking about the toilet drain.

Ordinarily, the toilet drain is larger than the sink drain, but that alone is not enough. It should be wide enough to hold the combined wastewater flow (both sink and toilet wastewater).

Failure to comply with this requirement could result in a burst-off which could be expensive to fix and deplorable for your household.

  • A common valve within a 1.5m radius

Your kitchen sink and toilet or shower drain can share a vent if they share a common valve that’s not more than 1.5 meters away. Usually, plumbing experts connect drain pipes in a home setting by installing a vent underground that allows water and sewage to drain freely without an airlock.

So, if the valve is within a 1.5m radius, your toilet and sink will share the same drain.

can a toilet and bathroom sink share the same drain

In Summary: Can A Toilet and Sink Share the Same Drain?

For the toilet and sink to share the same drain, these conditions must be met:

  • The toilet pipe should be larger than the sink drain and large enough to contain the combined flow.
  • You must install a common valve about 1.5m from the two drains. The common valve connects the two pipes and prevents airlock.

Understanding the Common Vent and its Purpose

Generally, it’s costly running two separate drain pipes (toilet and sink drain), and most homeowners prefer to combine them. For that to happen, you must install a common vent to allow wastewater to flow through both drains without forming an airlock.

In that case, the vent allows the smaller drain (the sink drain) to empty into a larger drain (the toilet drain).

Overall, the toilet vent makes it easier for wastewater to flow out of your home into the furthest end of your drain system (sewer) once you flush the toilet or run the sink water.

Can A Toilet and Bathroom Sink Share the Same Drain?

Ordinarily, the chance of an airlock forming within the drain and preventing the flow of wastewater down the sewer is higher when you combine the toilet and the bathroom sink drain.

You can, however, avoid all that by fitting a common vent about 1.5 m away. This vent ensures that the sink drain freely empties into the toilet drain (the larger drain).

So, to answer the question, yes, a toilet drain and bathroom sink can share the same drain as long as you fit a sink drain within an acceptable range (1.5m radius).

The other condition is that the two pipes should fit to form a perfect union and that the larger drain should be large enough to bear the combined floor. If that’s not the case, you should separate your toilet and bathroom sink drain and only allow them to empty at the same sewer but not share any other connection.

Can A Toilet and Bathroom Sink Share the Same Drain

Can A Toilet and Kitchen Sink Share the Same Drain?

Just like it is the case of the toilet and the bathroom sink, the toilet and the kitchen sink can share a drain if you fit a common vent to prevent airlock. That’ll ensure the wastewater flows smoothly and there are no backflows.

Can I Drain My Sink into The Toilet Vent?

The biggest issue with combining the sink and the toilet drain is the airlock. If airlock forms between the drain, the wastewater won’t flow.

Expert plumbers, however, counter that by installing a common vent about 1.5 meters away from the drains, which prevents airlock. As a result, it becomes easy for wastewater to flow to the furthest end, the sewer, when you flush the toilet or open the sink tap.

So, the short answer is yes; you can drain your sink into the toilet vent.

Just ensure the toilet vent is within reach (within a 1.5 m radius) to avoid an airlock (remember, an airlock could lead to wastewater backflow, and you wouldn’t want that happening.

Can Two Toilets Share the Same Drain?

Most homes and hotels have more than one toilet, emptying their content in a commonplace alongside bathroom and sink drain.

If the toilets are on the same side of the building, they can share the drain. But if they are opposite sides, you’ll need to install two drains to quickly vent out the waste and direct it to the sewer.

Nowadays, contractors employ Y connectors to connect toilet drains back to back and prevent backflow. 

can two toilets share the same drain

Can Two Sinks Share a Drain?

Combining two sinks in the same drain system is possible using special valves and pipes. However, you may have to vent the sinks separately to prevent airlock and the possibility of wastewater backflow.

As for double sinks, they’ll all require separate drains, but they can share the p-traps, thus cost-saving.

Do Sink and Toilet Have to Match?

It’s always easy to combine a sink and toilet drain if the two match. That allows you to fit a sink valve that prevents airlock and eventually encourages the combined wastewater to collect down at the sewer.

However, that doesn’t mean that the two drains have to match. The toilet drain can be larger than the sink drain and not vice versa to effectively hold the combined wastewater flow without bursting.

People Also Ask

1. Can A Tub and Sink Share the Same Drain?

Most bathtubs and sinks share the same drain pipe. It happens all the time in homes and hotels. The only issue is that the connection has to be expertly done to avoid the backflow of wastewater due to an airlock.

2. Can A Toilet and Sink Share a Vent?

The biggest issue with combining the toilet and sink drains is that airlock can form due to the pipe’s diameter difference, resulting in wastewater backflow. That, however, is preventable by installing a common vent. It allows the toilet and the sink to share a drain.

3. Do Sink and Toilet Water Go to The Same Place?

All wastewater in your home collects at a septic tank (at home) or the nearest sewer. That includes water from your kitchen and bathroom sink and toilet water.

4. Do Toilets and Sinks Use the Same Drain?

Ordinarily, the toilet and sink pipes are two separate drains that empty their content at a commonplace (the sewer). Nowadays, however, homeowner prefers to combine the two drains as it is economical.

The secret is to ensure you first install a common vent to prevent airlock. Airlock mostly leads to a backflow of wastewater.

5. Are Toilet Drains and Kitchen Sink Drains Connected?

All drains in your home connect to a shared network of pipes that empty at a commonplace (sewer). So, yes, your toilet drains, and kitchen sink drain are connected. That’s unless you choose to install two separate drains, which can be costlier.

6. Can You Put a Toilet Where the Sink Is?

Given that all the drain pipes in your home connect to a shared network and empties at the sewer or septic tank, you can rearrange them. That means you can swap the sink and toilet. However, the job is too technical, which means you may have to hire a plumbing expert if you don’t have the technical know-how.

Can A Toilet and Sink Share the Same Drain? Closing Thought:

As seen, it’s possible to combine the toilet and sink drains with a common vent and fit it within 1.5m. But still, the larger pipe (toilet pipe) should be big enough to contain the combined floor. Doing so saves on plumbing costs as you only buy a few pipes and fixtures.

Also Read:

Let Us Know How We’re Doing!

Did this expertly prepared resource answer your question?

Do you have another question about home maintenance, home improvement projects, home appliance repair, or something else?

Get more information, send in questions and keep the discussion going by contacting the I’ll Just Fix It Myself company customer service team at at 1-800-928-1490 or Email us at [email protected]