Update: A PUB gentleman called me up a few days later and told me his guys found a blockage in the sewers along the street and cleared it. And gave me his mobile to directly call him if any more blockages or smells happen again. Cool.
Me to LTA hotline, 29th September, Monday, 10.22pm: "Hello, I want to report a nasty smell along Upper Serangoon Road, at the junction of Simon Road. I think it may be sewage. I can see a trail of water on the side of the road running for quite far. Maybe a sewage truck spilled it or a pipe burst somewhere. It is very smelly."
LTA hotline: "Thank you for the feedback. We will inform PUB."
The next day…
PUB hotline calls me, 30th September, Tuesday, 1.21pm: "Hello, you reported a smell at Upper Serangoon Road? Did you see any water flowing out of somewhere?"
Me: "Er, yes, I reported it. No, I did not see any source, just the smell. And a trail of water along the road side."
PUB hotline: "Ok, I will send my man down to investigate now."
Me: "I made this report last night. I think the water dry up already."
Maybe I was two days too early for the new Municipal Services Office hotline.