The answer to 'how does bathtub work' is that a bathtub is a plumbing fixture used for bathing, typically made of porcelain, acrylic, or enameled steel. It is designed to hold water and allow a person to sit or recline in it for cleaning and relaxation. Bathtubs are connected to the home's plumbing system, with hot and cold water supply lines and a drain that connects to the sewer or septic system.
When you turn on the faucet, water flows into the bathtub. The drain at the bottom of the tub allows the water to exit when you're done bathing. Most bathtubs also have an overflow drain near the top to prevent the tub from overfilling. Bathtubs can be installed as a standalone unit or as part of a larger bathroom suite with a shower.