Sanitary sewer utility piping carries waste water and sewerage from residences, institutions and industries to treatment plants for processing.  Sanitary sewer piping should not be confused with storm sewer piping, which is completely different in terms of water source and quality, flow characteristics, and design parameters.   Even though closed and buried pipes are used in their construction, sanitary sewers are considered open channel, gravity flow systems.  The slope of sanitary sewer piping is designed to provide flows that will prevent any stagnation and settling, but not be so fast as to scour the pipe interiors.  This is typically a flow rate of less than 10 feet per second in most applications.  Sanitary sewer systems are designed for what is expected to be a theoretical peak flow condition, assuming most system users would apply waste water into the utility at the same time.