Unfortunately Jocko has posted the diagram for the Mk2 which is different to the Mk3
The one I posted was for the Mk 1, for JeffB, as he has a Mk 1.
Apologies Jocko, I looked at the link you posted, saw it was 2007 and assumed it was a Mk2.
It appears we're back on the Mk3 trail now though so now harm done by all the well intentioned posters.
Another little trick that I know has worked is to pop a Milton sterilising tablet into the washbottle. It has worked on other marques running considerably higher power, hence hotter engine bays resulting in the washbottle being in a hot ambient temperature - good conditions for bacteria to grow.