I just noticed it about a week after I rented it. I was going through the receipts and viola...a little spark went off and I started ranting.
The clerk said that no one had ever questioned him on it before and vowed to figure it out before I cam for my next tool renatl (about another week)
EBUCK
My suspicioun is that it is to cover a disposal fee that the business is forced to pay for disposal of some kind of hazardous material. Probably something like oil soaked kitty litter that they use to clean up oil spills with, or used oily rags.