To protect backflow, ice containers must:

In the context of preventing backflow, it is essential that ice containers have good drainage and an air gap. Backflow can occur when contaminated water is siphoned back into the potable water supply, potentially causing health risks.

Having good drainage ensures that any excess water or melted ice does not accumulate and create a pathway for contaminants. The air gap is a critical component because it acts as a physical barrier that prevents any liquid from flowing back into the container and ensures that there is no direct connection between the ice container and any potential source of contamination. This design minimizes the risk of cross-contamination and safeguards the ice, which is often used in drinks and food preparation.

The other options do not effectively address the need to prevent backflow. Sealing containers tightly might help keep out debris but does not specifically address the issue of preventing liquid from entering the system. Filling containers only halfway does not prevent backflow and does not affect drainage or the presence of an air gap. Storing containers in the microwave does not relate to backflow protection in any practical sense and does not address the contamination risks associated with improper storage or drainage.