On Thu, 29 Mar 2018 18:39:34 +0100
Harry Bloomfield wrote:

Plumber's Mate

Plumber's mait

was suggested to me, as able to seal the impossible. I
spent two days struggling to get a seal on two wash basin drains, I
tried PTFE, Boss White - neither worked, but PM did first try. Its a
none setting sort of mastic, difficult to get it to stay put on the
thing you are trying to seal, it prefers to pull back off on your
fingers

Wet your fingers.