Which component is responsible for preventing sewer gases from entering buildings?

The trap is the component that plays a crucial role in preventing sewer gases from entering buildings. Traps are U-shaped sections of pipe designed to hold a small amount of water, creating a barrier that blocks foul odors and gases from the sewer system. This water seal effectively keeps harmful gases, which can be hazardous to health, from infiltrating the living spaces.

In contrast, while the vent stack helps maintain air pressure in the plumbing system and allows sewer gases to escape above the roof, it does not create a barrier against them entering the building. The sump pump is used primarily for removing water to prevent flooding in basements and is not involved in managing sewer gases. Similarly, a drainage cleanout is a maintenance feature that facilitates the removal of blockages in the drain system and does not prevent gases from seeping into the building. Hence, the trap is the essential component that ensures safety by keeping sewer gases at bay.