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If you plan on rough plumbing a toilet, you need to know what size pipe to use. Today, all toilet pipe sizes are standardized, so you don’t need to look very far to find the right sized pipe to rough in a toilet.

Toilet Drain Pipe Assembly

A toilet drain pipe consists of three main parts: the soil pipe, closet bend and drain line. The soil pipe is a vertical pipe that installs in the flange, the other end fits into the closet bend. The main drain line runs from the outlet side of the closet bend to the home’s main drainage system, also called the drain stack.

Toilet Soil Pipe Size

Your typical soil pipe is 3 inch diameter schedule 40 pipe used throughout the home as the main drainage pipe. This pipe slides up into the flange and is usually cemented in place because both the flange and the soil pipe is PVC or ABS pipe.

A 4×3 closet bend or reducing closet bend has a 4-inch inlet and 3-inch outlet.

The closet bend is also 3 inch pipe, however there are various closet bend sizes. A reducing closet bend configuration, or a 4×3 closet bend, has two different sized ends to connect two different sized pipes. One end, in most cases the inlet, is 4 inches wide, this mounts to the toilet, and the outlet end is 3 inches in diameter.

This is so the closet bend can connect to a larger 4 inch diameter drain pipe and 3 inch pipe. Most 4×3 closet bends mount directly to a 4-inch toilet drain. If the closet bend is going to mount right to the toilet, use a 4×3 closet bend.

Some closet bends allow a 3 inch pipe to slide into one end, while the same end can mount to a 4 inch pipe. This is very useful when mounting closet bends to different types of pipe.

Toilet Drain Pipes

After the closet bend, a series of pipes leads to the home’s drain system, called the main stack. These pipes are typically 3 inch diameter pipe, either PVC, plastic ABS or iron pipes. ┬áSince 3 inch pipe is generally connected to the end of the closet bend, most closet bends have at least one 3 inch diameter connection.