All of your descriptions are hardly unskilled, those take a good deal of education, practice, and in the case of plumbers legal certification that probably involves an apprenticeship. It's absolutely a skilled profession.
In my youth I briefly worked for a temporary agency and did a bunch of odd tasks to fill in when needed. The least skilled thing I did was for a newspaper: sliding racks of newspapers from a conveyor belt onto a long table, watching this massive table vibrate the newspapers for a solid couple of minutes (to prevent pages from getting stuck together as the ink dried), then throwing in the day's collection of laminated ad inserts into each set, and then pushing the boxes onto the next conveyor belt down the line. Training was thirty seconds of instruction.
I would call it 'labor' because it doesn't need any adjectives or qualifiers. It's just work, somebody laboring at a task.
The Nazis started with the disabled, trans, gays, and autistic. The Jews came after the political dissidents.