The big deal is if there’s so much need for overtime, then there’s a greater need to hire more janitors. At time and a half pay, they could have hired another janitor and saved the budget that extra .5. Poor management. Imagine how messed up the rest of the budget is.
That said, Zang is one smart guy. Nowhere else could he bring in that kind of money for that skill level.
Keep in mind this is a govt., union job, in the most liberal city in the People's Republic of California. The employees get lots of sick days. They can't schedule more people because Zang is picking up hours when people call off unexpectedly. It is probable that most of the employees refuse to come in to work extra hours on short notice, leaving Zang as the go-to guy.