Interestingly enough I have a comparison. My stepson just called me earlier today to fill me in on a job promotion at the hospital..this is what happened:

For the past week or so during his shifts new hires were coming up to him and stating they were told he was supposed to train them. The first few times it happened he shrugged it off, even though it meant that he was spending an extra couple hours or more completing his rounds and paperwork. But when he realized it was a pattern he called a meeting with his supervisor and basically said while he was happy to do it once in awhile, if it was going to be added to his list of everyday duties then he needed a pay raise. So now while he's training he makes an extra $10 bucks an hour and gets overtime-time and a half-when he stays past his shift because of it.

People will take advantage when you don't draw a line unfortunately.