Hot take: my buddy said 'just ask them to rinse their plates' and that advice cost me 4 months of misery
He swore the sink situation would fix itself if I just said something nice once, so I did, and my roommate in Fort Worth looked me dead in the eye and said 'cool' and kept stacking crusty bowls for another 4 months. Anyone else get advice from a friend who has clearly never shared a bathroom with a stranger?
Honestly the "just say something once" advice is only half right. Asking nicely works when the other person actually cares what you think, but if they hit you with "cool" and nothing changes, that's not a communication problem, that's a them problem.
One nice ask is fine. After that it's fair to say the sink staying nasty is a dealbreaker instead of just hoping round two goes better.