Hi Mark.
I know some people use Miltons for cleaning all their glassware, available at any chemist. Comes in liquid or tablet form. It's the stuff used for sterilising babies bottles etc. Check here
http://www.milton-tm.com/healthpro/what_is_milton.htm
The residue is supposed to be harmless (to humans anyway).
It's great for cleaning ceramic diffusers of algae (should you be unfortunate enough to get it

) if left to soak overnight and rinsed well in the morning. Come up sparkling.
Though I'm sure with the experience of others, diluted bleach would be just as good if rinsed well.
Chris.