hey geoff... you should probably clean your tank. granted you've by now probably sucked any of the loose stuff into your fuel filter (you do have an inline fuel filter, right?) but, getting a clean tank is always a good thing. and, since it was most likely half filled (or half empty
) the part that will be rusty you can't see by looking thru the hole.
peace,
the other geoff (just call me heffay) 
Your are right Heffay, I do have an inline filter. Seems to be remarkably free of rusty bits and general gunge. But I think your right on the cleaning front. It will have to be a winter job as I am having to much fun riding the bike just now to start taking bits off (Actually got a few winter projects but never mind)

.