The last task as a refueler for star cruisers
If the professions have already seemed terrible to you, then the task of refueling warp drives will truly disturb you. Human spaceships travel long distances by diving into the warp, the realm of chaos.
However, if humans were to enter there unprotected, they would immediately have demons on their backs, tearing their souls apart. That is why the ships are protected by a gellar field, a kind of bubble of reality meant to shield against the warp.
The warp drive must also be refueled with a highly toxic fuel. Humans are employed for this purpose, dressed in thick lead suits and continually pumped with a drug cocktail to travel to the actual drive.
In Rogue Trader, you have your own ship:
Because they not only have to carry a heavy box – extremely strong radioactive radiation exists around the drive that slowly breaks down the body. While you are on your way to the destination, your body deteriorates, muscles burn, and flesh simply falls off the bones. There is no way back.
If you are now wondering why servitors are not used for this: built tech and cybernetics are expensive, human lives are not… To excuse this, the worker is even considered a “ritual sacrifice”. But as a small consolation, at least some of the “more humane” leaders still resort to Servitors.