http://w25rxxn62dgix7qdbw4ot37m2y4ty7kxfrinspw4ce7jzse7pb6rhaqd.onion
This is not legal advice, but a reasonable, though possibly prohibitively complex, way to ensure anonymity may be to somehow acquire and use a Tor-only amnesiac operating system like Tails or Qubes with a Whonix disposable VM on an uncompromised burner device where you'll encrypt your message locally before ever connecting the device to the internet. When you connect to the Hush Line Onion service, it should be on an uncompromised network you do not own, to which you are not related, and...