Sound advice Barry, we have never had a waste tank leak reported before.
The wash basin drains through the bottom of the light tube and into the wall unit and flexes as the basin is swung into the wall cavity, this waste pipe has been reported to get hard and brittle – I changed mine when I fitted a new splashback/basin. This pipe and its entry to the waste tank can be checked by removing the panel with the air vent in at the side of the toilet.
The sink outlet and the route of its waste pipe can be checked by removing the panel at the back under the sink ( on my SG so presumably the same on SK). This pipe heads towards the inspection hatc under the bottom drawer as pointed out by Barry.
So with some good lighting and a little agility there are good access points for observation to trace the source of the leak.
I sincerely hope that there is nothing major wrong with the tank and hope that it is one of the pipes or joints pointed out by Barry. There should be a protection guard on the shower outlet in the boot.
Fred