What is the primary reason for installing a trap in drainage systems?

The primary reason for installing a trap in drainage systems is to prevent odors from entering buildings. Traps are crucial components of plumbing systems that retain a small amount of water, effectively creating a seal. This water barrier acts as a blockade to prevent sewer gases, which can contain harmful and unpleasant odors, from rising through the drain and infiltrating indoor spaces.

While the other options address aspects of plumbing, they do not capture the primary function of traps. Improving water flow is not the main role of a trap, as its purpose is more about maintaining a seal than enhancing fluid dynamics. Separating solids from liquids is a function of certain types of systems but is not directly attributable to the trap itself; traps are designed to hold water rather than separate waste components. Facilitating maintenance tasks may be a secondary benefit of certain plumbing designs, yet it does not represent the fundamental purpose of traps in preventing harmful odors from entering living and working environments.