I have a concealed cistern behind MDF, which has been tiled.
I am fitting a new flush valve in place of the old syphon. It's mostly done, but I need to recess the button. That needs a 40mm hole through the tiles and MDF, in place of the existing rather ragged 30-35mm hole.
What's the best way of doing that? 40mm drill will tend to wander. I have a 1/2" belt sander, but that'll take ages. Any suggestions please?