Reach out to the local Porta Jon / Porta Potty company. They will have "grey water" tanks and may have some converted or willing to convert to black water as well.
The folks that immediately go to "call the county govt" kill me. If you have access to this type tank there is absolutely no need to get the local officials involved. And no, they most likely will NOT have the answer, and when they don't, the answer will almost certainly be NO.
Not being cynical, I have spent a large part of my career working in municipal govt, currently work in a position where I work very closely with the community development office. They do not have all the answers.
My favorite local story is a local building inspector who would not sign off on a plumbing job. When the plumber quizzed him he said "because this job isn't done by the book" (the Georgia book of building code). The plumber asked: Do you have the book with you? The inspector pulled it from his trunk. Plumber asked him to show him where in the book it showed his job was incorrect. Inspector said it was his interpretation of the code.
The plumber then asked the inspector to flip to the front page of the plumbing code, and asked him to read who authored it. The author's name matched the name on the plumber's business card.
The plumber wrote the code. Again, don't leave your decision to the interpret of an inspector or code official when there is no need to bring them in the picture.
