Ever get an on-site pump out of your gray/black tanks?

I wasn't sure whether to tip the guy since he works for the CG and it is part of the service the CG provides in their daily rate. I usually tip most service industry people pretty well. But this was all new to me, and the guy was in a hurry to get on to the next pump site. Besides, how do you hand someone money who is wearing huge yellow vinyl gloves that are covered in.....well, you know.