i feel for you in your situation. i don't think i could do that job, for me it would be like working in a research lab looking after the animals, feeding and cleaning them, and knowing what fate is awaiting them. in the same way you give the drinkers what they want, knowing that each drink could be their last one.
on the other hand i would probably feel more sorry for the little mice in the labs as they didn't choose to be there. the drinkers know what they are doing and the potential consequences and still choose to drink.
maybe that thought helps.