Full practice instructions on package. The elastic cord winds around the base, and the ball locks into the base pocket. https://www.academy.com/shop/pdp/unique-fill-n-drill-tennis-trainer The elastic cord winds around the base, and the ball locks into the base pocket. Just fill with water to anchor the base. It sets up virtually anywh The trainer is a great teaching tool for beginners and intermediate tennis players. Some tennis trainers are not heavy enough to not move on the ground and some tennis trainers are too hard to fill up. The Unique Fill & Drill tennis trainer for tennis training includes a solid base that stays in place when filled with water. Elastic rubber cord winds around base, ball fits securely into base pocket. The trainer is a great teaching tool for beginners and intermediate tennis players. The elastic cord winds around the base, and the ball locks into the base pocket. The Unique Fill & Drill tennis trainer for tennis training includes a solid base that stays in place when filled with water. The Unique Fill & Drill tennis trainer for tennis training includes a solid base that stays in place when filled with water. It sets up virtually anywh Patented Fill & Drill Tennis Trainer fills with water to become heavier than concrete based tennis trainers. The trainer is a great teaching tool for beginners and intermediate tennis players. The Unique Fill & Drill tennis trainer for tennis training includes a solid base that stays in place when filled with water. Fill-n-Drill Tennis Trainer. The Unique Fill & Drill tennis trainer for tennis training includes a solid base that stays in place when filled with water. Color:Blue Fill & Drill Tennis Trainer: When filled with water or sand, the base becomes heavier than any other Tennis Trainer on the market. The elastic cord winds around the base, and the ball locks into the base pocket. The Unique Fill & Drill tennis trainer for tennis training includes a solid base that stays in place when filled with water. It sets up virtually anywh Tourna's Fill-n-Drill is the easiest tennis trainer to fill up and its the heaviest on the market. This tennis ball return system has a weighted base (is a hollow base that you fill with water and screw on the cap) and a strong rubber cord that returns the ball after you hit it. The elastic cord winds around the base, and the ball locks into the base pocket. The elastic cord winds around the base, and the ball locks into the base pocket. Elastic cord wraps around base and ball locks into pocket for storage. The elastic cord winds around the base, and the ball locks into the base pocket. ITEM CODE: FD-1. very light and portable when empty, can be stored in players bags and taken along. The Fill n Drill Tennis Trainer is a great way to train alone, in your driveway or other open, paved area. Strong rubber cord returns the ball. Great teaching tool for beginners and intermediate players. The trainer is a great teaching tool for beginners and intermediate tennis players. The trainer is a great teaching tool for beginners and intermediate tennis players. It sets up virtually anywh The Unique Fill & Drill tennis trainer for tennis training includes a solid base that stays in place when filled with water. The trainer is a great teaching tool for beginners and intermediate tennis players. The trainer is a great teaching tool for beginners and intermediate tennis players. The trainer is a great teaching tool for beginners and intermediate tennis players. It sets up virtually anywh The Unique Fill & Drill tennis trainer for tennis training includes a solid base that stays in place when filled with water. The elastic cord winds around the base, and the ball locks into the base pocket.