What is the minimum diameter for lavatory waste outlets?

The minimum diameter for lavatory waste outlets is indeed 1 1/4 inch. This size is specified in plumbing codes to ensure adequate drainage and prevent clogs while accommodating the flow from the lavatory sink. A larger diameter helps to remove wastewater quickly and effectively, minimizing the risk of buildup that could lead to blocked drains.

Larger pipe sizes, while they may allow for better flow rates in high-demand situations, such as in larger commercial fixtures, are not necessary for typical residential lavatory applications. Therefore, while options with larger diameters are available, they exceed the minimum requirement and are not deemed necessary for standard lavatory installations. Smaller diameters, on the other hand, might not provide sufficient flow capacity, which can lead to drainage problems over time. Adhering to the minimum standard of 1 1/4 inch ensures both effective drainage and compliance with plumbing codes.