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Plumbing

Building Drain

In Plain English

The main drain pipe inside a building that collects all the wastewater and directs it to the sewer line outside.

Definition

The lowest horizontal drain pipe within a building that receives discharge from all soil, waste, and drain lines and carries it to the building sewer outside the structure. The building drain runs from the base of the main soil stack to the point 2 to 3 feet outside the building foundation. It must be sloped to maintain a self-cleaning velocity.

Example

The building drain was undersized for the restaurant's grease loads, requiring upsizing from 4-inch to 6-inch pipe.

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