Concrete pumping line systems can be cleaned by propelling a clean-out ball through the line with air or water. "Soft" balls are designed for use when blowing out lines with water or sucking the ball back through the line. "Hard" balls are more suitable when using "air" instead of water. For sizing, the cleanout ball MUST always be larger in diameter than the line it is to clean - a tight fit is necessary to retain pressure. CAUTION: Only fully trained personnel should attempt to use Clean-Out Balls.