A plumbing riser diagram is used to segregate plumbing systems for potable water, waste water, storm water, sewage, and so on in order to define exactly where the different pipe is placed and what it is connected to in terms of appliances, drains, other building systems, and so on. The term "riser" refers to any vertical pipe that carries water from one level to another. In a plumbing system, risers are usually between 20 and 50 feet long. At the top and bottom of each riser, there should be no more than two openings called "stops". These stop holes allow the insertion of pipe-cleaning tools so they can be used to check the inside of the pipes for obstructions or damage. Risers are used wherever there is a change in elevation or direction of flow. For example, if you were to drain your bathtub and there was a riser under the bathroom floor connecting to the kitchen sink riser, you would use risers like these in order to maintain a continuous flow of water without having multiple valves in multiple locations.