With few exceptions, where should horizontal drain piping be provided with a cleanout?

In plumbing systems, cleanouts are essential access points that allow for inspection, maintenance, and clearing of potential blockages within the drainage piping. When it comes to the placement of cleanouts in horizontal drain piping, the best practice is to have them located at the upper terminal.

This location is strategic because it allows for easy access to the piping system for maintenance tasks while minimizing the potential for clogs to go unnoticed in the system. By situating a cleanout at the upper terminal, it also facilitates easier drainage of any accumulated debris or buildup that might occur along the horizontal run of the pipe.

While cleanouts at lower terminals, midpoints, and junctions can be valuable depending on the specifics of the drainage system, having a cleanout at the upper terminal provides a more effective means of ensuring that the entire horizontal section of piping remains accessible for service and can be efficiently cleared if necessary.