Shower tile grout cleaner

[neilb]

I have white ceramic wall tiles in the shower with white grouting. I believe that the grout is actually some sort of white silastic. The tiles are easy to clean but the grouting is going black in places and I have tried a miraid of things to clean this blackening off but to no avail. Today I tried Selleys "Rapid Remove" cleaner but I shouldn't have wasted my time. Any ideas ?
Neil.

[Honorary Bloke]

Usually have good luck with a mild chlorine bleach solution, 3 or 4 to 1.