So, here, you can get a certificate of inspection; they check tank (no way to visually see anything with drain field), they pump the tank completely out, make sure baffle and all is intact; then they fill with gray water, to the top, and time the rate to drop below the discharge. Then, they issue a certificate of inspection. If I remember right, they refilled again, and timed again, until they got to 500 gals of added and perked water, or the daily usage of a 3 bed room home. It only took about 15 minutes per add, and the drain field was given a clean bill of health
Edit; the water was added directly to the tank, not through the plumbing.