That has a great deal to do with your location. Plumbers in Texas don't do nearly so well.>>>>>>>>
Here in Eastern South Carolina the owner of the plumbing company does ok but it is common to see ads for building maintenance jobs asking for someone who can do plumbing repair, carpentry, electrical and is certified in heating and air conditioning and they seldom offer more than twelve an hour for this superman, often less.
Same here, and there is a lot of competition for those jobs. Maybe things are different in NYC where Clemenza lives, but around here, those jobs pay about the same as in your area.