What is the fixture unit for a 1 1/4" waste pipe?

The correct choice identifies that a 1 1/4" waste pipe is assigned a value of 1 fixture unit. This understanding is based on plumbing codes and standards that define the fixture unit values for different types and sizes of plumbing fixtures and pipes. The hierarchy of fixture units provides a standardized way to calculate the load on a drainage system, ensuring that pipes are sized appropriately for the fixtures they service.

A 1 1/4" waste pipe is typically used for smaller fixtures like sinks or lavatories, which generally have lower waste flow rates compared to larger fixtures like toilets or showers that would require larger pipes and more fixture units. By assigning 1 fu to a 1 1/4" waste pipe, it allows for effective planning and design of plumbing systems while maintaining proper waste flow without the risk of clogs or overloading.

The other options would suggest higher values, which would correspond with larger pipes or additional types of fixtures not suitable for 1 1/4". This reinforces the standardization seen in plumbing design and application, ensuring safe and efficient waste removal.