Cleanouts must be installed at each change of direction in a building drain when the angle of change is:

Cleanouts are critical components in plumbing systems that allow for the inspection and removal of blockages. The requirement to install cleanouts at changes in direction is based on ensuring proper maintenance and accessibility for plumbing systems.

When there is a change in direction of 135 degrees or more, the flow of waste can create challenges in drainage. Such changes can contribute to larger potential blockages and make it more difficult to clear clogs without access points. By installing a cleanout at each change of direction of this degree or greater, plumbers provide necessary access for maintenance. This is essential for keeping the drainage system functional and preventing build-up that could lead to serious plumbing issues.

In contrast, less abrupt changes such as those under 135 degrees may not necessitate a cleanout, as the flow can maintain better passage without significant risks of clogging. Therefore, the code specifies that cleanouts should be provided at changes of direction of 135 degrees or more to facilitate effective cleaning and maintenance.