Depends on what the "plumber" is doing. Certainly there are plumbing tasks (eg pipe sizing for a chemical plant) which I would qualify as engineering. I would q

Depends on what the "plumber" is doing. Certainly there are plumbing tasks (eg pipe sizing for a chemical plant) which I would qualify as engineering. I would qualify it that way because they probably had a series of constraints (must transport X liters of substance Y / second at Z temperature, fit within service routing of the structure, minimize cost, etc etc) which they optimized against. I think a plumber who, say, fixes a sink, is not doing a similar process. Between those points lies the gray area of subjectivity!