Hi cactusflower!
Thank you for the question as it is something high on my list of non-polluting activities.
Many hail the modern sewer system as the savior of our civilization because, they think, we've successfully developed a system to remove and treat solid waste in a safe, non-polluting manner. Upon closer examination, this proves to not be the case although it's better than what we had before, which was essentially nothing.
The idea behind composting or waterless toilets has been around for many years. In simple terms, you are working with nature to break down feces into a harmless, non-toxic substance that can be placed directly into the earth. With continued research into understanding support of the bacteria needed for successfully breaking down human feces it has become relatively simple and inexpensive to build composting toilets. This is not your typical "out-house" and the best part is, they don't stink!
There are many variations of the design from compact, self-contained units to large, multi-bin designs. There are manufacturers offering ready-made units along with organizations offering plans to construct your own. There's even a gentleman here in my area that will build to order and deliver to your site.
Many organizations have taken the idea into poverty stricken areas of the world, including many parts of Asia, to provide sanitation assistance to those who lack the means or knowledge to prevent polluting their ground and water.
A great deal of information on the subject is available on the Internet.
Composting Toilet World