>>11398450
>>11398458
If she's stationary, you can just put a shower nozzle above her that automatically sprays her with (pure cold) water and soap after every use. Also, the feeding could be with an automatic dildo that she has to deepthroat for nutrition. This both trains her and teaches her that she has to accept her throat getting violated, and denies her any taste or agency.
She'd start completely restrained with a mouth gag, but some restrains would be released once she learns to keep a proper position, accept all abuse, thank the man after each use etc.
Also it's much hotter if it's not just a random slave but a coworker that fell from grace, either because of bad results and behavior, or because she's just so cute and unapproachable that her coworkers voted her the public toilet. This works even better in a highchool.