Sounds like the job is "fixing Motors," which may include all sorts of devices. The fact that some of these motors are for processing human feces may be unexpected. Since you're so good at fixing them, then all the work comes in (I imagine other places are: "no thank you.").
Seeing how now you are working on these particular objects, then a new set of protocols may be in order; probably none available to the company/boss because they never thought this market niche would come about.
I recommend bringing this up to management (as you have), requesting new protocols be put in place. Including--of possible--a more thorough cleaning of said pumps before you even get your hands on them (like your bleach idea).
Since it is falling on deaf ears, then you report to OSHA and see what they say when they eventually come to investigate.