Can't pass this thread by without adding my ten pen'orth.
I have been using the cheapest supermarket own brand biological washing tablets in my cassette for a long time now ( don't use non-bio ). Chuck in 1 or 2 with a pint of water when you do your cassette and they break down the yucky stuff and keep it smelling sweet, including normal toilet paper, and you can empty it anywhere as there's nothing in there that you would not put down your sewer system at home.
They also cost about a third of the price of conventional toilet chemicals and are available anywhere. You can also use them in your flush tank and your grey waste tank, saves having several different chemicals on board.
Hey vwalan, you know those gas burning engines you saw? well I used to machine the engine blocks for them in my last job. Just a nice size for your truck, a 91 litre V18 with the most humoungous spark plugs you've ever seen, about 2500 horsepower at 950rpm. We used to send them all over the place to have the genny's put on them and sometimes they were built as a complete package in a shipping container. Drop it on site, plug it in, job done!