Is the drain of the toilet bowl and the shower drain connected? (SURPRISING Answer!)

You probably take the presence of a shower and a toilet in your bathroom for granted, but they are actually two separate systems with very different requirements. However, it is possible that the drains of these two systems are connected. This is not always allowed and can lead to undesirable consequences. Read on to find out more about the connections between shower drains and toilet drains and their potential impact. Let’s take a look into this.


What is the Difference Between a Shower Drain and a Toilet Drain?

A toilet drain is meant to be used to collect black water and a shower drain is meant to collect grey water. 

Grey water is water that has been used for cleaning and can contain soap and other residues. Shower water and water from the sink are grey water because it is unclean water but it doesn’t contain that many harmful bacteria. 

Black water is water that has been used for flushing the toilet because it contains waste that needs to be flushed away. This waste is unsafe and should be removed from the house as soon as possible. 

The last type of water is rainwater. Rainwater can be used in a house. For example, it can be used to flush the toilet or to clean the car. This type of water has to be stored separately from the other types of water. It is generally collected in a water tank. 

 Sometimes these types of water need to be separated so that it is easier to process them. Water processing facilities can work more efficiently if both types of water are separated. In some areas, they even want to collect rainwater separately. This makes sure that water processing facilities don’t get overwhelmed when a big rainstorm breaks out. The water is processed before it gets released into rivers and oceans. This makes sure that the water in these places remains clear.  

Why Are Shower Drains and Toilet Drains Connected?

In some older buildings, it was not required to separate the grey and black water. For this reason, they just connected the drains as this was easier to install and took up less space. It is quite difficult to change this connection as you have to open up the floor of the bathroom. 

In some areas of the USA it is not required to have a separate drain for each type of water. This can be seen in rural areas that have their own septic system or areas that have less strict requirements. We can expect that more and more areas will start to require a separate connection though.

When Should You be Concerned About Connected Shower Drains and Toilet Drains?

If you find that a shower drain and a toilet drain are connected, then you should look into your local requirements further. In most instances, this is fixed when the bathroom is being renovated. 

Plumbers will use the right size of drain and install them at the correct angle. This will make sure that everything works properly.

The main drawback of a connected shower and toilet drain is that the shower can backup if there is a clog in the drain. This can mean that dirty water enters your home. It can be quite dirty to clean this up. Toilets have a toilet bowl where the dirty water can be stored in. Showers don’t always have this and it can leak in your bathroom.

If there is a leak in the drain, more dirty water can go into the soil as the shower water can push the toilet water away. This can lead to contamination in your garden. In some instances, it will be necessary to dig up the soil to remove the problem from your garden.

How to Identify if Your Shower and Toilet Drain are Connected?

To find out if a shower drain and a toilet drain are connected, you need to use a camera that goes in the drain. This can allow you to see how the drains are connected. You can also open the floor to see how things are installed. This is mainly done when a house is being renovated. 

Most houses also have building plans. You can check these plans to see how things were installed. If you don’t have them, you can take a look at when the house was built. Based on the building standards of that area, you can make an educated guess.

If you hear a noise in the shower when you flush the toilet, it can also indicate that both drains are connected. Air and water are transported in these drains and you can often hear this moving around.

Another way is to take a look at the plumbing stack downstairs. If you only see one drain coming down, it might indicate that both drains are connected.


The presence of a shower drain and a toilet drain connected together may be an indication that there is an issue with the drainage system. A poorly connected drain can introduce bacteria into your house if there is a clog. This can cause a lot of damage.  It can also lead to problems in your garden or the water processing facility. Check your local rules to make sure that you have the right setup. If needed, you will have to adjust your installation. This is quite challenging to do as you need to use the right drains. A plumber can help you with this.

More and more attention is being paid to wastewater as it is important that it is processed properly. One of the ways to do this is by collecting the different types of water separately. This can require a lot of infrastructure but makes sure that our waterways are clean and safe. Water from the rivers and oceans evaporates and rains down on us. Because of this reason, it is important that we take care of the quality of the water. This is why there are some rules around your plumbing installation.

We have outlined how you can add a toilet to existing plumbing here.