Call the county health department. In WV the county I talked to said only portable tanks were legal for long term use. A non-portable tank was only legal for 90 days, and you had to be making progress on a septic system.
In Oregon I stayed at a campground that had a repurposed oil field frac tank for the poo poo. They pumped it as needed. An employee told me they had similar rules, as long as the tank is portable it was OK. Now this tank was a standard 500 barrel (20,000 gallon), but you could drain it, and pick it up with a winch tractor. Get the rules before you buy.
These rules are crazy, yes?
