For even the smallest campers: SaniPottie Portable Toilets - already a big seller in the US. Great for caravans and motorhomes, trailers, boats, camping, cottages, trucks, bedside, potty training, work sites and more! Compact tanks - lots of capacity.
Accesses self-contained 12 litres (3.2 gallon) freshwater supply. 10.6 litres holding tank, compact size to fit about anywhere.