I`m changing the bath and want to keep the taps and the pop up waist bits. The problem is that when i take out the plug part of the pop up waist i am left with a swrewed in thing that disconnects the underneath part of the pop up waist. it looks like i need a realy wide screw driver to undo this, i have tried to undo it with a chissel but its realy stuck. is there a special tool to unscrew it?