Which of the following is not considered plumbing?

On-site sewage disposal is not considered plumbing in the traditional sense, as it typically pertains to the management and treatment of wastewater rather than the direct installation and maintenance of plumbing systems that provide water supply and drainage. Plumbing generally involves the systems that supply water and distribute it to fixtures, as well as the systems that carry wastewater away from buildings.

Drain cleaning, water supply piping, and fixture installation all fall directly under the category of plumbing work. They are essential components of a plumbing system, focusing on the delivery of clean water and the removal of waste, which are the primary functions of plumbing. On-site sewage disposal, on the other hand, deals with the handling of sewage in a broader environmental and regulatory context, which distinguishes it from standard plumbing practices.