Can a Bath and Toilet Share the Same Drain?

Plumbing systems are very complex, making it difficult to install a new bathroom without extensive plumbing experience. Although many homeowners understand the plumbing basics, most don’t know how to set up bathroom piping during renovations, causing them to ask many questions, such as “Can a bath and toilet share the same drain?” Fortunately, Babe Plumbing, Heating and Air created a short guide to teach you everything you need to know about bath and toilet drain sharing.

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The Difference Between Bath and Toilet Water

Although your bath and toilet water end up in the same place (the city’s sewage system or your septic tank), they are extremely different. Toilet wastewater is much less sanitary and more likely to carry diseases. Although used bath water isn’t the cleanest, it’s more sanitary than toilet water and rarely carries disease and other hazardous contaminants.

To distinguish the two water types, plumbers call toilet wastewater black water and used bath water gray water.

Black Water

Black water is the most dangerous water type and often contains feces, urine, and other waste that can cause significant health issues in humans and animals. Cities strictly regulate black water disposal and prevent it from seeping into water sources.

When setting up a bathroom, black water must flow into the sewer lines or septic tanks. Sewer treatment facilities handle the disposable process once a septic tank reaches full capacity.

Gray Water

Gray water isn’t as toxic as black water, but still isn’t ideal to drink. Cities don’t regulate gray water as much as black water but still prevent it from mixing into fresh water sources like streams, lakes, and rivers. Experts classify shower and bath water as gray water.

Although some people use gray water to water plants and wash their vehicles, it’s best to dispose of it since it can still contain potentially dangerous chemicals.

Can a Bath and Toilet Share the Same Drain?

So, can a bath and toilet share the same drain?

Since toilets and baths don’t use the same water type, most people want a separate drain for each fixture. However, they can share the same drain if you set up a common vent and connect their existing drains with PVC connectors.

Common Vents

The common vent prevents backflow that can cause unsanitary water to flood your bathroom. Black water flooding can cause extensive water damage while increasing the likelihood of a waterborne infection such as cholera.

Common vents prevent incompatible water like gray water and black water from forming an airlock as they flow out of their drains, stopping backflow. Installing a common vent is a must if you want your bath and toilet to use the same drain.

PVC Connectors

Toilet drains are typically much larger than bath drains and are incompatible with each other unless you connect them via PVC connectors. These connectors are two- to three-inches wide and allow both fixtures to flow into the same main drain.

Keep in mind that you need to cut the ends off the sink and toilet vents before attaching them to the PVC connector. You’ll also need to install sink traps to stop sewer gas and wastewater from leaking inside your house.

It’s important to note that the connection between the bath and toilet can’t exceed a six-foot radius. Failing to do so prevents the valve from transporting water into the drainpipe. If you can’t maintain a six-foot radius, your bath and toilet can’t share the same drain.

You’ll also need the following tools to connect the toilet and bath to the same drain:

• Three-inch PVC pipes and caps
• PVC adhesives
• PVC saw
• Shower strap
• Three-inch PVC bends

How To Connect the Bath and Toilet to the Same Drain