What minimum size is required for a main sewer line?

The minimum size required for a main sewer line is 4 inches. This size is specified to ensure adequate flow capacity and to manage the volume of wastewater generated by typical residential and commercial plumbing systems. A 4-inch diameter pipe has sufficient cross-sectional area to accommodate the drainage needs of multiple fixtures, including sinks, toilets, and showers, without risking blockages.

Using smaller pipe sizes may lead to slow drainage and increased potential for backups or clogs, which can result in costly repairs and sanitation issues. Therefore, the Uniform Plumbing Code establishes the 4-inch minimum size to promote reliable and effective sewer system operation.