I've had to assist fixing an older manure tanker, years back before they had clean out doors on them, and the pumps were inside the tank towards the front, a very poor idea, what was worse anyone who'd ever buy one like it, if the pump locked up or quit the tanker couldn't be emptied, most of that vintage had holes cut into the sides somewhere to let the manure out so they could be worked on, the one I had to help with was used for hog pit manure for decades, the stench was so bad I almost fell over and that was outside the tanker, the repairs had to be done inside them, had to be the worst job I'd ever helped with up to then.
The next one I never worked on, helped with or had to do anything with, was just at the shop the day it came in. A rendering truck called into that shop, its winch wasn't working, which is mounted at the top, front of the box, inside to pull the dead stock into the truck, the winch brackets had broken and the winch couldn't be used, at the time it pulled in, it was a miserable hot summer day, and it turned out the truck was almost full of ripe bloated dead cows and pigs. The driver thought he was saving the guys the hassle of using a ladder to reach the winch, just crawl over the dead stock, sit on a dead cow and do the repairs...........................I was told later the guy that did it had a close pin on his nose and was sent home for the day when he was done. Was around another shop that had to do the same thing for another rendering company, but that time the truck was empty, washed out and the stench was still so bad, you could hardly breath when standing beside the truck, I told them both they were absolutely nuts for every agreeing to do the job in the first place, no matter what they got paid.