Not sure about the line "All campers are expected to dump gray and black into the pit toilets. There is no outside opening for a honey wagon."
I could see them potentially making this arrangement for the campground host/work camper, but certainly not for all campers. A vault toilet only holds so much and with everyone dumping their 30-50 gallon BW & GW tanks in there, it would overflow frequently and need to be pumped all the time.
As others have said, for FW, fill a bucket and use a DC transfer pump to get it into your FW tank. If they let you put BW & GW into the vault toilet, a macerator would be easiest.
But the first thing you should do is talk to your employers - whoever owns the site. What have previous work campers done? Where is the nearest dump station? Is there a honey wagon service nearby?
