What is the purpose of the main stack in multi-story buildings?

The main stack in multi-story buildings is crucial for effectively carrying waste and ventilating gases. Its design facilitates the removal of sewage and other wastewater from various points within the building, ensuring that these materials are transported safely to the building's drainage system. This stack also serves to allow air to enter the plumbing system, which is essential for maintaining proper pressure and preventing the siphoning of traps that could allow harmful gases to enter living spaces.

The ventilation aspect of the main stack is particularly important as it helps to manage odors and ensures that gases produced in the waste disposal process are safely vented away from the building. This not only maintains a healthier indoor environment but also supports the overall functionality of the plumbing system by allowing for the free flow of wastewater.

While the other options touch on aspects of plumbing systems, they do not directly address the core function of the main stack. For instance, reducing water pressure is primarily managed through pressure-regulating valves, and water distribution is more related to the supply lines rather than the main stack's primary purpose. Supporting plumbing fixtures visually is not a function of the main stack, which is mainly hidden from view within walls or utility spaces.