I used to live in a fairly nice neighborhood in which the largest, nicest home was owned by a plumber. The house was huge, a real McMansion. So I think if you own a plumbing business (as opposed to just being an individual plumber), you can do quite well.
I live in the Los Angeles area and my best friends husband is a plumber. He makes about 500K a year. He does big contracts. He employees 4 guys. She’s a hairdresser who owns her own shop and makes about 100K. Both are high school gradutes. Pretty damn good for a public school education.