late 14c. (from c.1100 as a surname), "a worker in any sort of lead" (roofs, gutters, pipes), from Old French plomier "lead-smelter" (Modern French plombier) and directly from Latin plumbarius "worker in lead," noun use of adjective meaning "pertaining to lead," from plumbum "lead" (see plumb (n.)). Meaning focused 19c. on "workman who installs pipes and fittings" as lead water pipes became the principal concern of the trade. In U.S. Nixon administration (1969-74), the name of a special unit for investigation of "leaks" of government secrets.
When a person has a blockage in their sewage system they often try to fix it themselves by adding an acid or a base such as Drano in an attempt to dissolve or dislodge the problem. These chemicals can get into the plumbers eyes when the sewage is splashed during the repair. The plumbers skin during the repair does come into contact with the sewage water. The owner of the toilet might not report to the plumber they have already tried Drano a highly caustic base .