The answer to 'how does drain work' is that a drain is a pipe or opening that allows water and other liquids to flow out of a sink, bathtub, shower, or other fixture. Drains are an essential part of a home's plumbing system, helping to remove wastewater and prevent flooding. Drains typically connect to larger sewer pipes that carry the water away from the home.
Drains work by using gravity to pull the water down through the pipe. The pipe has a slight slope that allows the water to flow downward. Most drains also have a trap, which is a curved section of pipe that holds a small amount of water. This trap creates a seal that prevents sewer gases from coming back up through the drain and into the home.