I'm in NC. I'm on orange mud/clay. I'm building a 2 bdrm house but I had the land perked for 4 bedrooms for the future, you never know. That would have required a 1000 gal tank and because of the clay, an extra 50ft of drain pipe per bdrm. My house looks down on a creek so the only place to put the drain field was uphill.
Then I told them 1 of the bedrooms would be in a different building, both buildings within 50 ft of the tank.
Because the 3rd bedroom is in a separate building, I'm required to install not 1 1000 gal tank but 2 1500 gal tanks. I guess most the work is done in the first tank and the 2nd tank just sees black water. When the second tank fills, the pump goes on. I think that's what they told me.
The county health folks are great. It took 7 weeks and later found out it could have been done in 2 days by a private soil scientist, for extra $ but, nice people and helpful!
I'm old, single and live alone. I tried to bet the county guy that, in my lifetime, I couldn't fill both tanks and that i bet the pump might never turn on.
Quote is well over $10K.