I've previously posted about using two 35 gallon tanks in my pickup truck (one fresh, one not-so-fresh) for replenishing my camper via a water pump and macerator.
Last week, I had a different problem - I was camping somewhere that doesn't have a dump station for at least 30 miles in any direction, so I didn't really want to have to take an hour long drive just to dump sewage. But I had access to a toilet...just not one I felt comfortable running my macerator's black hose into.
So I bought four water containers at Wal-Mart. Two for fresh water (6 gallons each, rectangular, and greenish), two for gray/black water (7 gallons each, more square, and blue). I obviously wanted to be able to tell them apart.
The lids on the square blue container have a built-in spout that is screwed into the top. You can unscrew that and, via fittings purchased at Home Depot, put a hose fitting on it. I then could pump waste into it via my macerator. It was no accident that each container was slightly larger than the total capacity of the toilet.
I used the other two containers for hauling fresh water back to the camper and dumping it in the gray water tank via their spouts.
This was not as pleasant as my preferred way, but it worked and was not messy - provided you can lift the full water containers (7 gallons of waste is heavy!).