I have to change my bath mixer taps, but before I do this to give me enough space I have to remove a circular dish about 6\\\" that controls the bath plug (up and down) and all the bits at the back including the black control cable. It is situated where the bath overflow is. The dish also has a small hole in so it can still act as an overflow. I have not seen one of these before and would appreciate some help, how do I take this thing off? cheers