What mechanism should be installed where drain tile discharges water to daylight?

The correct choice is the one-way flow valve because it is specifically designed to prevent backflow while allowing water to flow out of the drainage system when it needs to. When drain tile discharges water to daylight, it is critical to ensure that water can exit freely without allowing any potential reverse flow from the external environment back into the drainage system. This is particularly important in the context of radon mitigation, as backflow could introduce contaminated water back into the system, potentially raising radon levels or contributing to other drainage issues.

Installing a one-way flow valve at this discharge point takes advantage of gravity and pressure differences, enabling efficient drainage and protecting the integrity of the drainage system. This is essential for maintaining proper ventilation and ensuring radon-affected water does not flood the system back, which could compromise mitigation efforts.

In contrast, mechanisms like a two-way flow valve could allow water to flow back into the system, which is not desirable in this scenario. A manual gate would require manual operation and could be left closed accidentally, while a drain cover does not have the functional capability to control flow direction and is primarily used to keep debris out of the drainage system.