How does a urologist treat casual painless priapism erections?

Here are some...: I'm unsure if what you experienced & reported fits the definition of priapism, which denotes persistent prolonged unbearable painful erection, which requires a timely medical intervention so to prevent its long-term adverse effect - erectile dysfunction. So, what you reported may present a normal but "longer" than usual erection. Clinically, check if you're on any drug which may affect erection.