Kirkland here. We use it at the stick house, which is on a septic tank. You gotta figure, if it's rated for septic....which basically never gets dumped/pumped....only when needed, then it is sure to be OK for a black tank that does get dumped. I also did the shake test with it, and it broke down within 10 minutes, to just a "milky solution" so I was happy. No problems yet!
