Urinal traps and floor drains downstream from a water closet must be ______ inches in size.

The size of traps and floor drains downstream from a water closet is important for ensuring adequate drainage and preventing clogs. A 3-inch size is typically specified for these components as it allows for the efficient flow of wastewater while accommodating the volume produced by the fixtures they serve.

Choosing a trap or floor drain that is too small can lead to drainage issues, such as backups or slow drainage, especially when considering the heavy flow that can occur from a water closet. A 3-inch trap ensures that enough water is carried away, reducing the risk of blockages and maintaining a sanitary and functional plumbing system.

In this context, while smaller traps could theoretically function, they may not be compliant with plumbing codes, which often specify the 3-inch size for proper operation in these locations to handle the necessary volume of effluent. Ensuring that plumbing fixtures are connected with appropriately sized drains is critical for the overall performance and reliability of plumbing systems.