I do (still) need to test mine also, but strongly suspect bath sink goes to the BLACK tank, as Black filled much too fast w/ a few preschool grand kids; contemplation says not necessarily bad, as books say you want the extra water to keep all liquid/ loose for easy draining. I also noted that (my) bath faucet has a hose connection threads. OTOH, the being FULL (as seen through toilet) really caught us by surprise, with (unnecessary fear of) overflow/ flood on the trip to the dump.
NEVER Good to be surprised by a full waste tank