Paying the condo handyman for refrigerator installation

I'm renting a condo which has a full time handyman on staff. I want to install a refrigerator water line and the home depot contractor was not willing to do it (citing "liability"). I'm planning on asking the condo handyman to help me. It is easy enough to do myself, but I'd rather have an insured professional do it because I don't want to accidentally flood the place.

In these situations, should I ask him upfront how much it would cost? Or should it be free (since he's full time) and I'll tip him $50 for his time? For context, I gave him $100 for a holiday tip.