Working on the flight line we used to get tipped ~$5 for dumping a lav, sometimes even $20 per dump. It was a nice perk during a day of sewage dripping down your arm. I never judged a crew that didn't tip though, as it was part of my duties that I was getting an hourly wage for.

I see the van in the same light. I tip a buck or two when I have the cash, extra when the driver does a good job. But I don't lose sleep if my wallet is empty and I can't pay up. On the flip side I've gone to the ATM and come back to the front desk to find a driver that I felt really deserved a tip.