Which fitting allows maintenance access in a piping system?

Maintenance access in a piping system is crucial for ensuring the functionality and integrity of the system over time. A cleanout fitting is specifically designed to provide this access. It allows for easy inspection, cleaning, and removal of blockages in the pipes without needing to disassemble extensive sections of the piping.

The cleanout fitting typically comes with a cap that can be removed to facilitate access. This design is particularly important in drainage and sewer systems, where clogs or debris can accumulate. By installing cleanout fittings at strategic locations in the piping system, maintenance personnel can quickly address issues that arise, ensuring the system operates effectively and reducing the risk of significant plumbing issues.

The other options, such as couplings, reducers, and 90° elbows, serve entirely different purposes in a piping system. Couplings connect straight sections of pipe or tube, reducers facilitate transitions between different pipe diameters, and 90° elbows change the direction of flow. None of these fittings provide the necessary access for maintenance, making the cleanout fitting with cap the clear and correct choice for facilitating maintenance activities.