What type of fitting is required at the base of a vertical stack to allow for cleaning?

The requirement for a cleanout fitting at the base of a vertical stack is crucial in plumbing systems. This type of fitting provides an access point that allows for the removal of clogs or debris that may accumulate within the stack over time. The vertical stack, which can transport wastewater or stormwater, is often subject to blockages due to sediment, grease, and other materials.

Having a cleanout fitting installed at the base enables maintenance personnel to easily access this area for cleaning without the need for invasive measures or extensive dismantling of the plumbing system. This improves the overall efficiency and function of the drainage system and helps maintain proper flow. Other types of fittings, such as elbow or connection fittings, do not offer this level of accessibility and thus cannot serve the same purpose effectively.