Like so many of the jobs described here, it was a summer job between high school graduation and leaving for college. My father pulled some strings to get me a job in a paper box factory, cleaning the huge printing machines. It wasn't that hard, but was incredibly dirty, and I had to take long showers when I got home. It also happened to be the first summer that I was sexually active, so I was super attentive to my grooming, and getting the ink off me wasn't always easy. The following summer my father got me the same kind of job in a different factory. The third summer I got my own job, and I made sure it was a clerical job in an office, but ironically it was in....a printing ink factory.
However, the dirtiest job I ever experienced was not as a worker. When I was working in Czechoslovakia many years later, I was asked for advice about marketing coal by the manager of a coal mine. For some reason, he felt that we should see the full operation, so I spent one whole day underground, dressed like a miner and dragging around heavy equipment through the water and sludge and coal dust. I wasn't doing any mining myself, but I have never been more exhausted at the end of the day. It greatly increased my respect for what a coal miner endures to make a living.