Toilet with internal composting container
A composting toilet is a simple, watersaving and logical alternative to the water closet we know. No need for a water supply, no sewers and no sewage treatment necessary.
For me it's even a very practical way to become a part again in the ecological live-cycle of soil-plant-food-digestion-soil.
The instructions provided in the instructables link is for a composting toilet with internal composting container.
Another solution would be to construct a simpe box with a hole and a lid with a bucket inside. This you could even use inside a house. The contents would then be disposed of on an external composting heap, always being covered up nicely with other material.