Which part of the tank should be covered with soap solution during testing?

The entire tank surface should be covered with a soap solution during testing because this approach allows for the detection of leaks throughout the entire tank. By applying the solution to all surfaces, including the top, bottom, and fittings, any escaping vapors or liquids can form bubbles in the soap solution, indicating a potential leak. This comprehensive method ensures that no area is overlooked and enhances the reliability of the leak detection process.

Focusing only on a specific area, such as just the top, bottom, or fittings, could result in missing small leaks that might occur elsewhere on the tank surface. Each part of the tank may present different risks for leaks, and a thorough assessment helps to uphold safety and regulatory compliance regarding underground storage tanks.