Which type of valve allows the driver/operator to relieve pressure from the hose?

A drain valve is specifically designed to release pressure or liquid from a system, making it ideal for the scenario described in the question. When the driver/operator needs to relieve pressure from a hose after water has been discharged, the drain valve allows for this action, ensuring that the hose can be safely disconnected or stowed without risk of residual pressure causing injury or allowing water to escape accidentally.

In contrast, a check valve is meant to allow fluid to flow in one direction only and prevent backflow, which does not facilitate pressure relief. A regulator valve controls the pressure to maintain a specified output pressure, but it isn't designed for direct pressure relief. Lastly, a flow control valve is used to adjust the flow rate of the fluid, not to relieve pressure. Therefore, the drain valve is the most appropriate choice for relieving pressure specifically from the hose.