How is urine stored?
In your bladder.
A person storing urine for later use in a urine-based drug test, can store the urine indefinitely, provided it (the urine) is in a clean, sealed container, and is stored in a dark, preferably cool place. The reason it is important that the urine be kept in an air-free and dark environment, is because of mold. A cool storage area will help prevent mold from growing.