In addition to supply lines and a faucet, a drain and overflow are essential parts of your bathtub purchase. Types of tub drains available include pop up, lift and turn, tower, chain and stopper, and cable operated. If you purchase a drain that uses a chain and stopper, you may want an overflow cover that will hold the stopper in place while bathing. An overflow cover, such as the one pictured below, is especially useful when you want to accommodate more water in your tub.
If you have little experience installing a tub or the necessary drain and overflow, you may find this video helpful. This video clip from the show, Bathroom Renovations on the DIY Network, shows you how to assemble and install a drain and overflow kit.