First, we are talking about a system that doesn't hold poo right?
Some state regulations, and counties for that matter, call grey water black water, but there are loop holes in most regulations.
The Federal Goal of the Pollution Control is to --> Not pollute waters and soils, so most Rules are designed for when black water and grey water LEAVE the building. Typically, the county agency has no authority if "waste water" does not leave the building.
First, the compost toilet makes compost. I have had several counties where I live tell me that poo is poo and it doesn't change, even in the warranty type incinerators or composting toilet units. Most people are better educated about their own poo than the county and really, who wants to manage poo when you can manage compost anyway?
So, as for the grey water, check your county building codes to see if they allow for using grey water for watering gardens. IF not, then look up "sand filters" which filter greywater so the only thing leaving the house is....filtered water.
Right now I am in a horn lock with my county as they are telling me a greywater filter is "illegal", which is simply not true and they have yet to produce a building code or Rule to prove that statement.
I prefer the compost toilet and greywater system for a lot of reasons:
1. Cost. A separate system costs around $500 for both the grey water filter and a compost toilet system. A Individual Septic Treatment System will cost around $15,000
2. Space. The ISTS would take about 100' x 45' of my yard, whereas the GW/Compost toilet are in house systems and take up less than 10' of space.
3. A ISTS is wasting my POO! I have been reading The Ringing Cedars and generational gardens are cool.
4. I don't care for the county people who like to bully people so I have less need to deal with them to get permits and increase my taxes.
I am sure there are more reasons I will think of later....