How to Plumb a Toilet | Toilet Vent Distance | Toilet Vent Pipe Size

How to Plumb a Toilet

Your new toilet, whether it is a two-piece or one-piece toilet, needs proper plumbing. Also referred to as venting, it's important to know how to plumb a toilet when you make a bathroom addition to your home. Learn all the basics here with our guidelines and refer to our toilet vent diagram for visual aid. Before we go over the infographic, let's nail down a few basics:

What Is a Plumbing Vent?

Did you know that all plumbing fixtures with a trap need venting? Without a proper vent, the plumbing won't perform as well, and you'll hear horrible gurgling sounds. The vent is a pipe that connects horizontal drain lines to the exterior air above. As waste moves through the line, the air is drawn in through the vent for smooth passage.

Toilet Vent Pipe Size?

It's typically recommended that you go with a 2" PVC pipe for the vent. This is according to the uniform plumbing code (UPC). It may not be enough, depending on how many fixtures you are trying to run off the vent. You should check with local building code requirements to be on the safe side. Take note that the international plumbing code recommends just 1.5".

Toilet Vent Distance

According to the UPC, the distance between your trap and the vent should be no more than 6 feet. In other words, for the vent to work properly, it needs to feed into the drain line within 6 feet of the trapways that connect to it.

Plumbing a Toilet

how to plumb a toilet diagram

There are many different ways to vent your fixtures, and you're going to want to cater to the factors present in your bathroom. The most common configuration is to feed 2" PVC down from the ceiling within the wall behind the toilet. The vent pipe connects into the toilet drain pipe.

Chances are, if you are plumbing a toilet, then you also need venting for a sink. The sink is connected with a 1.5" pipe that branches off the main vent line above the toilet. We are going to proceed accordingly with this guide as if you are doing both. If you have an unusual situation where you are only venting a toilet, skip the instructions pertaining to the sink, and ignore any of those components in the illustrations. To complete this project you're going to need PVC pipe, as well as DWV fittings and pipe. So let's get on with it. Here are a few sample configurations:

Example 1 (Pictured Above)

Through the floor, the toilet connects to the flange. The toilet flange connects to a 4" x 3" DWV closet bend, which then connects to a 3" combo (the image shows a sanitary tee, but it should be a combo). We left that mistake in there with the correction to illustrate how common of a mistake this can be. The combo connects to a short run of DWV pipe which connects to a 3" x 3" x 3" wye with a cleanout cap sealing the open end. The discharge end of the wye connects to the building drain.

Example 2 (Not Pictured)

Through the floor, the toilet connects to the flange and to 3" DWV, which then connects (hopefully) to a long sweep 90. You can do a wye with a cleanout cap sealing the open end. We recommend the long sweep 90 because it allows gravity to do a little more of its magic. The 90 connects to a run of 3" DWV that connects to a 3" x 3" x 2" wye. The 2-inch side of the wye connects to the vent mainline by way of a 2" street 45. The discharge end of the wye connects to the building drain.

Example 3 (Not Pictured)

Another common configuration you'll come across is a toilet that drains straight down through the floor. In this case, you would run the 2" vent pipe all the way down to the floor, then with a 45 street elbow, direct it towards the drainpipe where it connects through a 3" x 3" x 2" wye.

You can go with any number of configurations. Use these examples as inspiration for determining the best solution for your space. Good luck with your project, and if you need more specific help, reach out to us.

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Related resources:
1-Piece vs. 2-Piece Toilets
Elongated vs. Round Toilets
Measure a Toilet Rough In

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