Stress
If you're not cool with wallowing in filth or cramming your body into tight spaces for extended periods of time, you might be able to see how this job could be a little stressful. Not to mention the difficulty in finding steady work if you're a self-employed plumber, or the difficulty in scraping by on a meager living if you're just starting out at a plumbing company (plumbers at plumbing companies make about $10,000 less on average than those who self-market).
There's also the stress of continually coming home to a loved one who won't go anywhere near you because you smell like raw sewage. Which is worse than cooked sewage.