You can use a stopper that is made of rubber or plastic and can be locked into the drain. It has a rubber tube attached to the stopper. Once you shut down the water, you can pull up the stopper, make the necessary changes, and then submerge the stopper back into the tub. Also you can use a rubber stopper, as it does not require you to make a hole in the tub. There is a rubber ring that is attached to a clamp which is attached to the tub. The stopper is inside of this ring. As the water level rises in the tub, the rubber ring is pushed back and allows water to drain down the drain. Whenever there is no more water, then this ring is pushed back into the groove and blocks out of the tub.