A working FC lav should be a MEL item; the horror of even possibly having to use the same lav as the unwashed masses is simply too awful to contemplate. Can any amount of compensation truly make up for this? I should think not. Perhaps DL should pay for a few months of therapy to help the OP through an event that could quite possibly induce PTSD.
Added to that is the 'march of death' to the back and having to look at their faces - and expressions of disdain. There is a reason FC gets on first - so they can get into their seats and avert their eyes as the great unwashed marches to the back with paper bags filled with all of their worldly possessions and perhaps a live chicken or two.
But having to walk through that - both ways... To quote colonel Kurtz - "the horror, the horror".