Dow Corning 785 series for you then Tony, cheaper imitations will not do. And remove some grout from the bottom gap between tray and tiles, gives the sealant something extra to grab.
I find that the best about is Parasilico Sanitary N.
Its not dear and it does the trick.
I think there is a company that now sells it on Ebay.
The do them in a range of colours too.
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