To stop a tub from draining, first determine if the stopper is engaged and, if so, disengage it. If not, try plunging the drain by placing the plunger over the drain opening and pumping it rapidly up and down several times. If that doesn’t work, use a drain snake to manually remove any blockages. Finally, try using a drain cleaner, such as baking soda and vinegar, to dissolve any remaining buildup.