What is the minimum size for a main cleanout in a residential plumbing system?

The minimum size for a main cleanout in a residential plumbing system is 3 inches. Cleanouts are essential access points in drain, waste, and vent (DWV) systems, allowing for maintenance and clearing of blockages. As per plumbing codes, a 3-inch cleanout is generally mandated to accommodate the flow of materials and to allow effective access for tools required for snaking and cleaning.

This size ensures that a plumber can adequately manage typical obstructions that may occur in residential plumbing systems while maintaining sufficient drainage efficiency. Cleanouts typically need to be strategically placed at the base of vertical stacks and along horizontal runs to facilitate easy access for maintenance. While larger cleanouts may be used in specific scenarios or for larger building systems, the 3-inch minimum size is commonly recognized as the standard for residential setups.