After looking at all kinds of septic tank systems including earthship black water systems; I have found that all of these systems are really horrible. All require so much build and maintenance, and the idea of contaminating water to purify it again later just does not make sense. In nature we would just give it directly to the earth without any human made system (no water needed). So the only viable system I can recommend is dry composting toilets.
There are many ways to do this, but for those living in areas with winter it might be good to have a composting toilet or a system that holds more at a time, and a room to store it until Spring arrives. Remember that in order to neutralise any harmful pathogens it needs to be heated above 55 degrees celsius or stay for 2-3 years before being safe as a fertilizer (plant food soil). There are some rules here we all should learn. Either way this is great compost for fruit trees and berry bushes.
If you must have a fancy toilet the Nature’s head composting toilets are some of the most popular. In some cases there can be more advanced systems, but if possible, use wheelie bins that you can easily move around.