I was an apprentice drain cleaner with a local Roto Rooter franchise. Cleaned the main line under a trailer once. Toilet at each end of the trailer. The one furthest from from the exit backed up. The owner left it for a year, as the other one still worked. That end of the line was clear. Then called to have the 1 year old backed up section cleaned. Which meant crawling under the trailer, setting up the machine, removing the clean out cap _ as 1 year old poop plopped out_, and inserting the cable & cutter, by hand.
After opening the line, and putting the machine back in the van ( with an aged poo covered cable ) i rode with my head out the window all the way to the nearest car wash.
On another Roto call, i went to the crawl space under a kitchen at a WPAFB building. Where 4 inch pvc garbage disposal lines had repeatedly broken over the years. And it was 4 inches thick of moldy buildup. Had to use pieces of cardboard to push it into a vactor hose. Took 17 hours climbing over & under pipes to get at it all. Ended up throwing my new boots away. Never could get the smell out.