When the stopper inside the tub has given up the ghost, a temporary fix can work until you can repair or replace the old stopper. For your home bathtub, a simple inexpensive vinyl or plastic round stopper covers the drain to keep water in the tub. You can find these at grocery stores, superstores, hardware and home improvement stores. But when you can't get to the store right away, temporary fixes can also work.
For an emergency fix when you can't get to the store, create a makeshift drain stopper from items you may have on hand.
When the gasket has failed on your pop-up drain and no longer acts as a seal to keep water in the tub, plumber's putty offers a temporary fix until you can replace the gasket. Plumbers use this putty in drains and other fittings to prevent leaks.
Roll a bit of putty between your hands into a snakelike shape long enough to encircle the drain. Lift up the pop-up drain and cover the leaky gasket with the putty, closing the drain on the putty. This is a one-time fix, as you'll need to remove the putty when you drain the tub.
Washcloth in a Bag
Take a washcloth and set it inside a plastic bag. Squeeze or suck most of the air from the bag, sealing the ends if it's a sandwich or storage bag, tying the ends in a knot or using a cable tie to seal the washcloth in the bag. Insert the washcloth-in-a-bag into the drain hole and turn the water on. You may have to hold the bag and washcloth in the drain until enough water is in the tub to keep them in place.
Keurig Single-Serve Cups
Check the drain size in the tub, as Keurig coffee single-serve cups might just fit inside the drain to keep water in the tub. Simply set the cup into the drain hole with the top facing down to plug the hole. It might leak a bit, but it should last long enough so that you can take a bath.
Clean the rubber end of a toilet plunger with soap and water in the sink. Set the plunger over the drain hole in the tub, pressing down on it to form a seal. Remove the wooden handle -- if you don't want to look at it while you bathe -- and fill the tub with water. If the hole for the wooden handle goes all the way through, leave the handle in the plunger.
Marine Drain Twist Plug
Fisherman often have spare marine drain twist plugs in their tool kits. Meant for live fish wells or ballast tanks to drain the water after a day on the water, a drain twist plug works just as well to prevent tub water from draining. Twist the marine stopper plug into the drain clockwise by its T-shaped brass handle. Lightly pull up and twist it counterclockwise to remove. These only work if the twist plug matches the drain hole size.
Hold a large enough jam or other jar lid over the drain upside down. Turn the water on to fill the tub. Once enough water fills the tub, the suction from beneath the drain and the weight of the water should keep the lid against the drain to allow you to take a bath.
A plastic bag filled with water and sealed makes a quick stopper for the drain. Use a storage or sandwich bag and fill it with water, closing the seal. You can also tie a plastic bag that doesn't seal by wrapping a rubber band around the ends to keep it closed. Set the water-filled bag directly over the drain and fill the tub.