Muhl Tech Advanced Skills Batting Tee The unique brush cup ball holder gives a clean swish through the ball. Developed by a high school coach, the AST is made of durable polyurethane to stand up to high bat speeds and demanding team practices. The AST can be assembled or disassembled by hand for easy storage and transportation. It uses a hollow, canteen-style base that can be filled with sand or water and sealed with a rubber plug. When filled, the base provides weight for stability and when empty, the base is light and portable