Additional Information on DWV Systems
Drainage and waste systems rely on gravity to move solid and liquid wastes, so these piping systems must be installed at a slope toward the point of disposal. In the plumbing industry, this slope is called grade. Grade is also often referred to as slope or percent of grade.
Drainage and waste piping systems are designed with the grade engineered into the system.
In some cases, such as a residential plumbing, plumbers select the grades according to the applicable code.
In a system with proper grade, the liquid waste will flow at the right velocity, or speed, to scour the inside of the pipe, and carry away the solids.
• If the grade is too shallow, the liquid waste will not flow fast enough to scour the pipe and remove the solid wastes.
• If the grade is too steep, the liquid waste may flow too fast, leaving the solids behind.
In any of these cases, the pipe will soon become blocked with solid wastes.
The building drain is the main horizontal pipe inside a building. It is the principal artery to which other drainage branches of a sanitary system may be connected. It carries all sewage and other liquid wastes to the building sewer.
Any vertical pipe, including the waste and vent piping of a plumbing system, is considered a stack. A soil stack is vertical section of pipe that receives the discharge of water closet, with or without the discharge from the fixture. The soil stack is connected to the building drain.
A branch interval is a section of the stack. The branch interval usually corresponds to the storey height (the height of one floor in a building), but it can never be less than 8 feet long.
A horizontal branch is the part of drain pipe waste stack that receives the discharge from one or more fixture drain.
The building sewer or house sewer is the drainage piping that runs from the building's foundation to the sewer main or septic tank (private waste disposal system). It normally starts approximately 2 to 3 feet outside the building.
Building sewers are commonly made using ABS (acrylonitrile butadiene styrene) or PVC (polyvinyl chloride) plastic, cast iron, or vitrified clay (a hard, nonporous, clay) pipe.
Sometimes the pipes in a sewer are installed over a bed of gravel that supports them, preventing them from setting and losing their grade.
In some areas, plumbers lay the entire sewer from the foundation wall to the sewer main. In other areas, the municipal sewer crew may be in charge of the installation from the property line to the sewer main.
All operation associated with the building sewer are regulated by code. Always check the applicable codes when you are working on a sewer system.
Manholes must be provided for underground piping that is 8 inches or larger in diameter. They should be located at intervals not more than 400' of grade, elevation or pipe size.
To meet the applicable codes for traffic and loading conditions, manholes must have metal covers of sufficient weight and strength.
A public or municipal sewer is installed, maintained, and controlled by the local municipality or town.
The sewer main is usually located in the street or alleyway or within an easement on privately owned land. Sewer mains carry waste to the treatment plant.
Municipalities or towns usually install a 6-inch sewer laterally from the sewer main to the edge of each building lot. This lateral pipe connects the building sewer to the public sewage systems.