The plughole in my bathroom basin is leaking. The leak is between the plughole and the basin (i.e. through the circular hole in the basin in which the metal plughole is fitted), and it seems to me as if it needs sealing with some silicon kitchen/bathroom sealant. In order to seal it I need to remove, or at least loosen, the plughole fitting, but I can't see how, having removed the u-bend, detached and removed the plug actuator and the plug. I'm sure this is a pretty standard problem - could somebody please explain what I need to do?
This basin trim piece you are referring to is usually connected to the tail piece flange with a very fine thread. If has been in place for a long time, they can be difficult to remove. You will need to insert something like needle nose pliers in the top and hold the tail piece from the bottom and unscrew it. Clean out all the old plumbers putty and replace it by making a "rope" of plumbers putty in your hand, place it around the top edge of the hole in the basin, then reinstall the trim piece into the tail piece section. Tighten it so it pushes out all the excess putty, and is tight. Clean up the excess, return it to your can. Job done.