Link for Sewage disposal system information:
http://fapel.org/english/ansepti.htm
Here is another link to the care and feeding of septic tanks.
http://www.inspect-ny.com/septbook.htm
The invention of the septic process is fascinating.
Here in Massachusetts, there is a lot of work with enhanced nitrogen removal systems. There is a test center in Buzzard's Bay that has tested many systems extensively, here is a link to their website.
http://www.buzzardsbay.org/etimain.htm
A related matter in sewage disposal is grey water disposal. "Grey water" is water from sinks, bathtubs, showers and laundry.
Apparently, Art Ludwig of Oasis Design is a recognized authority on the subject and his advice is to forget about it unless you're willing to invest a lot of money and have a lot of grey water to dispose of (IIRC, greater than 3,000 GPD). His site, http://www.oasisdesign.net/index.htm, has a great deal of information.
Ludwig is the man when it comes to greywater. He even developed laundry soaps that are not only not bad for plants, they are even designed as fertilizer as well as detergent. Someone else is selling them now.
But you can't store greywater unless you do something like a constructed wetland the way the Earthshiptm people do in their greenhouses--and Mike Reynolds has recommended for outdoors in a book of his I once owned. Toby Hemenway in Gaia's Garden fell in love with a constructed wetland. It sounds like more than I want to do.
From experience, greywater turns into blackwater right quickly if you keep it in, say, the travel trailer's holding tank.
But teensy scale greywater recycling--on the order of tossing the dishpan's soapy water on the flowers by the back door--is perfectly reasonable. At least as long as you don't hit the same flowers every day.