Normally you don't. But at the bargain price of $50 for that work, and for an employee, it can happen on occasion. And I applaud you seeing it at a higher level, so to speak. With a good amount of sloppy/messy/inattentive-to-drips work out there, it's nice to hear about your appreciation.

As an aside, wen my father calls his plumber, I often hear him joking with him after receiving some advice, saying "honor thy plumber". There's some truth in that when you find a good one.

Whether plumbers or other workers.....

When they show up and do the job, no tip. If/when I have scheduling troubles or special concerns -- which is frequent given my care-giving situation -- and they show up having obviously juggled their schedules to accommodate my needs, I certainly do tip and verbally express my appreciation to them and their managers for the consideration given. My situation is probably unusual that way.

IMHO, ordinary work gets ordinary wages. However, when I think I've received exceptional service and/or consideration, I make sure the workers know from me that I've noticed. I know this is unusual because over the decades, various workers have told me so. On the other hand, conscientious service people have saved me loads of aggravation because of the extra effort they've put in from time-to-time. When they make a difference for me, I make a difference for them.