It's worth adding, that Singapore being clean is not a magical culture thing, but a deliberate government policy. Lee Kuan Yew writes in his memories that is took a lot of effort to make Chinese drivers stop spitting out of the cars for example and make the river not smell of shit.
This is true, but given 60 years it now has become part of the culture there. Maybe if you go out to the poorer places with SEA laborers, you can find betelnut chewers --but those are imported manual labor immigrants and not natives --though maybe you see them in the small islands.
Sure; Singapore (and Japan) do a lot to actively instill and maintain these conditions, from harsh punishments for drug trafficking, penalties for graffiti, good public education, a social safety net, affordable housing, government jobs programs, and so on. Basically, there's no need to whisper about how you need ethnic homogeneity to have clean streets.
