This Drain water vent plumbing plan is a system that allows air to enter the plumbing system to maintain proper air pressure, allowing sewage and greywater to be removed from a dwelling. Water produced by fixtures such as sinks and showers is called a drain, while water from toilets is referred to as waste. As the water drains, proper venting is required to allow water to flow freely and avoid the formation of a vacuum. Air needs to be passed into the waste pipe as the water runs down, either through a roof vent (external) or an internal vent. The drain water vent plumbing plan depicts the system that maintains neutral air pressure in the drains, allowing water and sewage to flow freely down drains and through waste pipes.