What is a common feature of a cleanout in plumbing systems?

A cleanout in plumbing systems is designed to provide a means to access the drain for cleaning and maintenance purposes. It is an essential feature that allows plumbers and homeowners to remove blockages and debris from the piping system without needing to disassemble the plumbing fixtures or pipes. This access point facilitates efficient and effective maintenance, ensuring that the plumbing system remains functional and reduces the risk of clogs and associated problems.

The other options don't align with the primary purpose of a cleanout. For instance, increasing pressure in pipes is not a function of a cleanout; rather, it would typically involve maintaining appropriate pressure in the system. Serving as a ventilation point pertains to vent pipes, which help prevent sewer gases from entering the living space, but this is separate from the functionality of cleanouts. Similarly, heating water is relevant to water heaters but has no relation to the role of cleanouts in addressing drainage and access issues. Thus, the most accurate description of a cleanout's role is that it enables access to the drain for maintenance activities.