Alternatively find some people who take joy in building robots to deal with the sewers and other joyless tasks. (Or some people who take joy in building robots that build robots that deal with such things.)
You missed another interesting option. Have robots (or pharmacology) which can reversibly alter a person's joy module(s) so as to take joy in dealing with sewers (or making/managing robots to do the same), and people who are fine with having the robots teak their joy-production neurons for a suitable duration of time.