Agree as well.
what does it prove, some water goes from inside into the tank? Not enough info for me to give a septic system the thumbs up.
I only use dye to verify there is no septic tank. In my area I need to verify if there is a tank before the lagoon or if it was a straight pipe to a ditch. Yes here in the rural areas finding a old farm house and sometimes a new house with a straight pipe running into a ditch is common.
Also used to find defects in plumbing, cracked tanks, failed EDA’s but never as a stand alone test.
20 years ago when I first started inspecting I worked as a sub contractor for The Building Inspector of America and that was how I was trained. Flush the dye down, flood the system the poke around looking for saturation, that’s it!!! and I got paid an extra $25.00. I literally did hundreds of septic inspection this way.