Don't forget that using grey water and humanure can give you so much more than a septic system ever could.

My kids asked the other day why cow, horse, and rabbit manure was good compost but human manure was not...

I explained that cows, horses, and rabbits didn't take pharmaceutical drugs and so their manure was good within a year or so while ours tends to take two years to get rid of the toxins that we willingly ingest. Another reason for this is that we humans often eat meats that are full of hormones that we were cannot process properly.

I guess what I'm trying to say is that you should seriously consider using your own waste to produce food rather than spending energy on a series of tunnels in the ground that will ultimately do little for you.

Of course, we have a septic system for my wife's peace of mind... and so have multiple acres to mow that could be better put to good use producing fruits and vegetables.