If the water takes a long time to drain from the shower, you must unblock the drain and clear the waste pipe. A build-up of soap and loose hair may clog the waste pipe, which prevents the excess water from draining. A blocked waste pipe can cause flooding from the shower and water seepage under the floor. The leaking water can damage the ceilings of any rooms below your bathroom. The blockage can be cleared simply and inexpensively.
Clear debris and dirt from the shower's water drainage hole.
Put on rubber gloves and eye protection, such as sealed goggles.
Slowly add 3 cups of caustic soda to 3/4 gallon of cold water. Caustic soda powder, also known as sodium hydroxide, is available at home improvement and grocery stores.
Mix the water and caustic soda very carefully with a wooden spoon. Caustic soda is corrosive. Do not splash it on your skin or anywhere outside of the plastic bucket. The solution will fizz and gradually heat up.
Pour the solution carefully down the shower drain hole. Leave it for 20 minutes. The caustic soda will penetrate the blockage.
Flush the shower drain with boiling water to clear the waste pipe. Repeat the process if the drain is still blocked.
Rinse off all equipment you used to thoroughly clean it.
Regular treatment with a half-strength caustic soda solution will prevent further blockages.
Open a window and keep the bathroom well-vented when using caustic soda. Always add the caustic soda to water and not the other way around.