It’s not everywhere in China either. I never saw that in newer cities like Shanghai and Shenzhen don’t have that quirk. But it is in Hong Kong and other parts of Southeast Asia.
I was always wondering when I see a sign saying to not flush toilet papers. Do you need to throw it in the trash can after wiping your butt? Because I always flush it, don't want to make the toilet room smell bad or give a hard time to the cleaning lady/boy!