Separate Septic tank for the main house. We were originally thinking of a common system, but the distance between the two and where it would need to be located to serve both locations was not really going to work. We also thought if we ever needed to split the lot and sell off or rent one building in the future, then I want separate utilities for each. A third factor was cost and timing. It probably would have cost me the same for one combined system as it would for two smaller separate systems. I also would have needed to have my main house planned, surveyed for grade, and the full system approved by the state health department with time bound permits that wasn't going to fit my timeline for when I will be ready to have the main house built.
