Which type of fixture typically requires a 4" trap?

A floor drain typically requires a 4" trap due to the significant volume of water it is designed to handle. Floor drains are installed in areas prone to water accumulation, such as basements, garages, and commercial kitchens. A larger trap size is necessary to accommodate potential heavy flow rates and prevent clogging, which is crucial for maintaining proper drainage and preventing backflow. The 4" trap provides adequate capacity to handle the discharge from multiple sources, ensuring efficient drainage during heavy use or emergency situations.

In contrast, fixtures like kitchen sinks, bathtubs, and showers typically utilize smaller traps, as their drainage needs are different. While they must adhere to specific trap size requirements according to plumbing codes, these are generally less than 4" due to their lower water discharge volume compared to floor drains.