aboleth wrote:
Thanks for the replies. I got the hosepipe in and did some carefully
directed spraying. The problem was partly that it there's a massive lag
in the system so I had to be very patient, not my strong suit.

Turned out that some hairline cracks in the grout were letting water
through, as expected. Going to scrape out any areas that look even
slightly dodgy and regrout.

Cheers,

John

I have a nasty way of sealing tiles to china..I uses a bead of silicone
first, then tile and grout over it.

Looks better than silicone alone, and won't let water through even if it
does crack.