NYC building codes set strict requirements for sewer line installation and replacement. Key requirements include minimum pipe sizes (typically 4 inches for residential, 6 inches for commercial), approved pipe materials, minimum slope requirements for gravity flow, cleanout locations and spacing, backwater valve requirements for below-grade fixtures, and connection specifications to the city sewer main. All sewer work must be performed by a licensed plumber and inspected by NYC DEP. Failure to comply with building codes can result in violations, fines, and required rework.