The plumbers are working downstairs installing a new bathroom. Plumber comes up, 'Please do not use the toilet for a few hours. Do not flush, I am disconnecting the pipe for a while.' I said OK.
A minute later I brush my teeth. I notice the water is draining slowly. I glug Drano down.
A minute after that knock, knock, KNOCK. 'Scuse, me are you using the water?'
Oh, no, please don't do that. I disconnected the pipe.
Don't the toilet and the sink use a different pipe?
No, is the same. Now it's wet there where I am working.
Oh, no, I poured Drano down too.
So that is the bad smell I was smelling.