What type of vent provides relief for pressure differences in drainage systems?

The correct answer highlights the function of a relief vent, which is specifically designed to equalize pressure differences in drainage systems. In plumbing systems, as water flows through the pipes, it can create negative pressures (suction) and positive pressures (pressure buildup) that may affect drainage efficiency and cause issues like slow drainage or sewer gas infiltration.

A relief vent allows air to enter the drainage system, balancing the pressure and facilitating the smooth flow of waste and wastewater. This mechanism is crucial for maintaining proper drainage function and preventing backflow or obstruction due to pressure variances.

The other options serve different purposes: exhaust vents manage air that needs to be expelled, soil vents are primarily focused on venting soil stacks, and stack vents act as a continuous outlet for gases from fixtures. While they contribute to the overall functionality of a plumbing system, they do not specifically serve to relieve pressure differences in the same targeted manner as a relief vent does.