What is the maximum number of water closets with a fixture rating of 3 that would be allowed on a 4-inch building drain laid at a slope of 1/4 inch per foot?

The maximum number of water closets allowed on a specific size of building drain is determined by the fixture rating and the capacity of the drain. In this case, a 4-inch building drain, when installed at a slope of 1/4 inch per foot, can accommodate a certain number of fixtures based on code specifications.

A water closet typically has a fixture rating indicating the flow rate and volume of wastewater it will discharge. A fixture rating of 3 suggests a moderate water usage. The Omaha Plumbing Code provides tables that outline how many similar fixtures can be connected to drains of various sizes.

For a 4-inch building drain, the code specifies a capacity limit based on the drain's diameter and slope. Therefore, if the calculation of fixtures for a 4-inch drain permits up to 72 fixtures with a rating of 3, then this number reflects that specific size and its ability to handle the wastewater flow effectively without risking blockage or backup.

Selecting 72 as the answer indicates an understanding of how the size of the drain and the fixture rating interact per code requirements.