Which of the following is essential to prevent overflow of concrete washout containers?

A concrete washout container is specifically designed to manage wastewater generated from concrete activities. For preventing overflow, it is crucial that the container is leakproof and well-maintained. A leakproof container ensures that any waste or runoff is contained securely, preventing contamination of surrounding areas and facilitating compliance with environmental regulations. Additionally, regular maintenance ensures that the container's structural integrity is upheld, which is vital for long-term effectiveness.

While constant monitoring and frequent emptying can contribute to proper management of the washout container, they do not inherently guarantee that the container will not overflow. Thus, the design and maintenance aspects are essential for ensuring that the containment system functions correctly and minimizes the risk of spillage, especially during periods of heavy use or adverse weather conditions. This makes having a leakproof and well-maintained container the most critical factor in overflow prevention.