Dead on - nice tip. I'll try it tomorrow.
Has to be a major suspect as my car started stinking of rotten eggs recently and even after letting Nickfit re-life the aircon it made no diference at which point they suggested the battery was shagged. Hhhmmm, recently charged to 12.8V and the indicator window showing perfectly healthy - I think not ! It was coming from the washer reservoir, which when siphoned out (cough), half the Gangees Delta came with it - as well several new life forms. Totally cured by repeated drains and a refill with a light dose of bleach left in overnight.
So it would seem i've sorted the resevoir but it is highly likely there is a major residue sitting behind the jets.
Note on the thread from 'steveisfrowning' - I used to use aerosol lighter refuel gas (available at all good Swedish Chemists) on those tiny bike carb air jets (in the blissful the days before injectors) as it cleaned them out and de-silted them a treat - may also work on the washer jets ?