[abb]

https://en.wikipedia.org/wiki/Vitrified_clay_pipe

Vitrified clay pipe (VCP) is pipe made from a blend of clay and shale that has been subjected to high temperature to achieve vitrification, a process which results in a hard, inert ceramic.

VCP is commonly used in gravity sewer collection mains because of its long life and resistance to almost all domestic and industrial sewage, particularly the sulfuric acid that is generated by hydrogen sulfide, a common component of sewage. Only hydrofluoric acid and highly concentrated caustic wastes are known to attack VCP. Such wastes would not be permitted to be discharged into a municipal sewage collection system without adequate pretreatment.

[meyer]

Thanks. To us pikers, it’s just plain ol’ clay pipe.