Can someone tell me what the correct technique is?
I originally had plumbers mait around the thread / nut under the basin and
also under the lip that is on top of the basin. Everything was watertight.
However I had to loosen the sink for tiling and since then can't get it
sealed again.

I posted on here about how to apply plumbers mait and was advised to use
silicon instead. I cleaned every thing up and applied silicon under the
lip, tightened every thing up and left it overnight. But it still leaks down
through the thread.

It is driving me nuts. I must have given it about 5 goes now, between the
plumbers mait and silicone.

Help!!!!