Ah interesting topic, we have a local fishing lake that has had a composting loo for a few years now, and seems to work very well as long as the last occupier remembered to use the saw dust
at certain times of the year there is bumper crop of WILD tomatoes and strawberries.
after reading LB's comments I dont think I will be partaking of the freebies this year though.
regarding using enviromentaly friendly fluids in the thetford loo been using them for years since we stayed at a farm site that had a reed bed sewerage system and was the only fluids allowed on site, I can confirm they are just as effective and cost little more than the blue stuff, and it is allways worth doing something to try and stop chemicals entering the water system.