I'm trying to fix a new toilet cistern to the bathroom wall of my Victorian house.
When I drilled through the wall tile to fix it, the drill bit went into a void between the bricks. The void is 24 cm. deep (so is probably going as far as the render on the outside.
I can't relocate the cistern (soil pipe etc.)
How can I fill this void in such a way that I can re-drill the hole and get a secure fixing ?