mwman wrote:
I just moved into a new appartment in a new high rise in Southern
China. To my surprise I noticed that ****there are no 's-traps'****
(='smell trap', 'grease traps, etc': the s- or u- shaped 'contraptions'
under each sink and all the drain lines.

That sounds very wrong. In this following case there may have been
s-traps in bathrooms but the water in them had dried up from disuse:

http://www.cbc.ca/news/background/sars/timeline.html

Hong Kong health officials say one person with SARS infected hundreds
of people in an apartment complex through faulty sewage pipes.

Hong Kong Health Secretary Dr. Yeoh Eng-kiong says the SARS-infected
visitor had diarrhea and as more people in the complex came down with
SARS and also had diarrhea, contaminated feces spread the virus through
the apartment's sewage system and then into bathrooms through drains
whose seals had dried up.