Building Drains: All dwellings built with indoor plumbing facilities that include toilet(s) have a drain system to allow effluent from the fixtures to combine into one single and larger pipe (typically 4″ diameter) called a building drain. The job of the building drain is to get the wastewater out of the dwelling and into the yard piping. Building drains in older dwellings were constructed by highly skilled tradesmen using hub and spigot cast iron pipe and fittings caulked with oakum (hemp twine) packed joints and sealed with pure lead. Building drains in newer dwellings are being constructed using solvent weld plastic pipe and fittings such as ABS or DWV PVC. All building drains installed under dwellings have 1/8″ to 1/4″ of fall per linear foot until it reaches the exterior side of the parameter foundation.
Sewer Lines aka/Yard Piping: Building drains are usually stubbed out past the foundation by about 2′ feet then transition to yard piping, at this point the pipe should be referred to as the sewer line. The sewer line diameter is consistent with the building drain diameter (or larger, but never smaller.) The length of the sewer line depends on wether the destination is an onsite private sewage disposal system (shorter lengths), or the line connects directly to a public sewer system (longer lengths). In older dwellings yard piping materials are the primary source of sewer line failure. Since cast iron was at a premium in the era when these older dwellings were constructed, it became standard practice to utilize substandard alternative materials such as: Asbestos Cement (AC), Orangeburg (OB), and Vitrified Clay (VCP) for construction of sewer lines. The aforementioned alternative pipe types were given a 30-50 year service life expectancy by the officials who approved them for use back then and I think it’s safe to say that they were only guessing. In newer dwellings with plastic sewer lines there is less problems with leakage due to the superiority of the solvent weld joint system. But beware, newer isn’t always better! In the past five years our company has responded to dozens of failed sewer lines in which the connection between the plastic upper lateral to the VCP lower lateral piping has suffered either a complete separation, offset, and/or shear breakage. We have also discovered many of the same type of failures at the connections where the cast iron no-hub two-way cleanout fitting (certain jurisdictions only) connect to the plastic upper lateral.