star wars - Why not use Droids for sanitation duty?

Why did the elite Stormtroopers have sanitation duties when they had millions of slave workers with no personhood-rights whatsoever?

Answer

Sanitation is a low-level duty. Basically you do it while you're a cadet, long before you get to go out and shoot people.

After years of training, FN-2187 had itched for some real action. Like other stormtrooper cadets, he’d rotated through several lower-level duties, including a janitorial assignment, but he hadn’t seen any real live-fire action yet.

_{^{Star Wars: Finn's Story}}

and

They were stormtroopers, but they weren’t quite, not yet. They were cadets, and as cadets they had additional duties aside from their training. Those duties covered everything from maintaining the armory to performing minor repairs on equipment to quite literally moving equipment from one location to another, often by hand but frequently with the assistance of the heavy-lifter droids, when whatever was to be moved was too big to be moved manually. They mopped the floors. They emptied the trash. They worked in the galley preparing meals.

_{^{Star Wars: Before the Awakening.}}

The goal seems to be that since you have a large force of cadet troops, you might as well get them to do something useful with their off-time. It teaches them about the base, about military discipline and procedures and about the importance of keeping their shit wired tight.