I hope not too long a post:
When I was a young person (22), I was a commercial diver, working for International Underwater Contractors out of Bayside, New York; one of the most memorable jobs was diving in sewers in Brooklyn, New York. I did this in 1967; I lived on West 10th Street in the Village back then, and thought that I would be a commercial diver for the rest of my life.
A new sewage treatment plant was under construction and our job was to open up or cut into valves between sewer segments, which would flood previously dry chambers and then use jackhammers underwater to destroy brick walls between the sewer segments, thus connecting everything for future routing to the sewage treatment plant. Operating jackhammers (horizontally) underwater is another story.
We would also cut the hinges off doors at sewage discharge points in the rivers, then close them, and weld them shut so that the sewage would no longer dump into the rivers.
This job paid the minimum for commercial diving because there was no depth involved (a maximum of 17 feet) but as we moved away from the manhole covers and the open surface of the big chambers into the tunnels (it was pitch black down there) we would get more money because we were under a ceiling. Some of the tunnels were completely packed full of “stuff” and we had to use a large suction hose to clean them out.
Our suits (dry suits, called Cousteau constant volume suits) would leak, as well as the helmet mouthpiece, so that the sewer water would get inside the suit and from time to time into my mouth. I was extremely sick for three days, because of the leaking mouthpiece, thought I was going to die. One day I rode the subway back to my apartment after my suit was flooded (I was all alone in the subway car that day). In addition, some interesting things happened one day when I went to sleep underwater while using the suction hose. How did I go to sleep? Well I was warm, it was dark, and I was floating weightlessly in a small confined space full of terrible "stuff".
Anyway, thank goodness, I was already diving in caves back then; it helped prepare me for the job!