What should be provided at grease duct cleanouts to ensure grease flows without pooling?

The correct choice emphasizes the importance of internal damming at grease duct cleanouts to prevent grease from pooling. Internal damming involves creating a barrier or modification within the duct system's cleanout opening that directs the flow of grease towards the grease trap or collection point. This design feature minimizes the chances of grease accumulating or stagnating within the duct, which is essential for maintaining proper airflow, reducing fire hazards, and ensuring efficient system operation.

Furthermore, effectively managing grease flow is critical for kitchen ventilation systems, as excessive pooling can lead to the buildup of flammable materials and increase the risk of fire. By implementing internal damming, the system can ensure a continuous and unobstructed path for grease to flow, thereby contributing to overall safety and functionality.

In contrast, choices mentioning a vertical lift, external access panels, or air pressure balance do not directly address the specific need to control grease movement within the ductwork at cleanouts, making internal damming the most effective solution for this scenario.