Red Green wrote:
Plumbers putty there I wouldn't have much confidence in. If you are
really desperate and at a loss go with silicone. I was once in that
desparation position. Did not have silicone, there is no pressure
being a drain but I did have time for the group to laugh here and
open tube of roofing cement handy. Sink underside black, cone black.
Never leaked afterwards.

And you thought I was kidding when I said I was no plumber :-)

No, but you're plenty smart.

Roofing cement is designed to stop leaks, right?