Do Toilets and Sinks Use the Same Drain?

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Have you ever wondered how sinks and toilets are connected?

Toilets and sinks can use the same drains. All you need to do is connect the lines underneath your bathroom and create a vent that allows waste to drain. Ensure you install a backflow prevention device to deter backflow from your appliances.

Is There a Difference Between Where Toilet and Sink Water Goes?

There is no difference between where the toilet and sink water goes to. Initially, water gets flushed down the drain. And every drain has its device pipe and a P trap.

Gravity speeds the water that is falling and this enables it to get over the P trap as fast as possible. And then into drain pipes. The moment it is there, water keeps flowing downwards through the tubes. The process takes place while supported by the vent system.

The drain pipes connect to the last pipe known as the lateral connection or lateral line. This is the biggest drain in a residence’s plumbing system. It has a diameter ranging from one and a half to two inches.

Moreover, the connection is the lowest duct in the plumbing system. It is covered up below the building and the garden. And just as the other vents in your house, lateral connection depends on gravity.

It helps to move the wastewater passing into it. The lateral line is installed in a slanting position. This will enable the waste to continue moving downwards. Furthermore, the water is also able to get out of your house through the garden and away from your residence.

It is at this section that the lateral lines connect with the metropolitan sewer pipe. The upper lateral is the point of the pipe connection in your home. The lower lateral is the area away from your property.

Therefore, It is through the lateral lines that the wastewater moves into the metropolitan sewer line.

What Happens to Sewage Waste?

Sewage water proceeds to the water treatment plant. In case the water moved in the direction of the sewer system, then it got to the plant. It will first go through a primary treatment procedure. It is at this stage the debris and other large particles are eliminated.

A secondary treatment procedure will then follow. This is where the organic matter gets discarded with the bacteria that do break down the pollutants. This happens before chlorine is used to disinfect water to eliminate bacteria.

At times the water undergoes a last advanced treatment. This is to remove any pollutants remaining. And which may result in problems in the given locale.

Like if there are large quantities of phosphorus or nitrogen in treated water. This can be harmful to the water bodies it’ll be put into and is therefore removed. After the water is treated, it is ready for all kinds of uses.

For instance, you can use the water for drinking purposes. Additionally, you can use it to irrigate your crops and sustain the aquatic animals. Still, it can get to where it started from, and that’s your shower

Can a Toilet and Sink Share the Same Drain?

A toilet and sink can share the same drain. A drain tube gets connected to a stack which becomes the vent running upwards through a roof. And a drain moving downward to the facility sewer.

Take note that drinkable water and sanitary sewer should not be directly connected. You also need to prevent the backflow of the wastewater from the device. This involves getting rid of the hose at your laundry tub.

And installing the backflow prevention device on a feed tube to the boiler and the external spigots. You need to ensure the condensate drains and your softener has air space. This also implies the dishwasher drain is held up high via the air gap created for it.

The reason for this is, in some conditions like opening the fire hydrant or the main water break, the water may siphon back to the mains. Moreover, it can drag the contaminants with it. For instance, the sewage, the stuff backed up in a laundry tub, or dirty dishwater.

Hence you should avoid lamenting about the need for backflow prevention. Be careful so as not to be the reason for contamination of the entire neighborhood. Nevertheless, if you need to integrate some greywater uses, you have to achieve some standards.

For example, you can decide to flush the toilet with water from the shower. Attaining the codes will help to prevent inadvertent contact with grey and drinkable water systems. You can get this designed and initiated by a skilled plumber who is well acquainted with grey water.

And if possible, consider draining within six feet of your toilet.

How to Connect the Sink and Toilet Drains

Connect the Drain Pipes

Start by connecting the sink’s drain pipes to those of the toilet. Use a sweeping y connector between two to three inches. Make sure the sink drain runs through the washroom drain from the top.

A two-inch gap for the sink drain needs to go upward from the three-inch horizontal pipe. This is to avoid problems regarding backflow.

Cut out Three-inch Section of the Drain Pipe

Do this while tying the two-inch sink vent. Use PVC glue and prep liquid to securely grip the connection.

Cover the Three-inch Drain Pipe

You need to cover the end of the pipe before you connect it to the primary sewer duct. Flush the toilet and then recharge the pipes with water to assess the connection. With this, you will also be able to discover if there are any leakages.

Can a Toilet and Shower Share the Same Drain?

Your toilet and shower can share the same drain only if the connection is done the right way. Also, you need to confirm whether the positioning of every item prevents backups and is up to the standards.

Even though it is not wise to link them to a similar waste trap, you can connect the different waste pipes to a common duct.

You can do this through wet venting. Though, you need to first check if it is recommended that you do so. There are also good reasons for connecting a shower and toilet drain like as follows;

It Is Cheap

The devices in your bathroom should be connected to your residence’s sewerage system. And you can take the drain lines from every plumbing fixture and operate them in their direction. That is, towards the main sewage outlet.

The costs of doing this are much higher compared to when you introduce a common vent. And connect all the faucets to it. Therefore, when they share a drain, it will make the budget more sensible and you will also save on time.

The Process Is Convenient

A shower and toilet sharing a drain isn’t only a question of saving extra cash. It is also more convenient. When you handle the fixtures in the bathroom as distinct lines towards the primary sewage outlet it will be hard on your side.

You will have tons of work regarding the planning and implementation phases. Besides, if you do not connect the toilet and shower to a similar drain, you will have to find a way to fit different pipes. And it is for all the appliances in your residential structure.

In other cases, the way you fit extra PVC ducts in a crowded tube network also matters. When you connect toilet and shower lines to a mainline by using a single vent, you lessen the time for planning and installation.


As noted, toilets and sinks can use the same drain. Just ensure you install the backflow preventer to deter waste from flowing back. Remember, having proper drainage is important and you need to be at the forefront to ensure the system works well.