So how do flies get in there? On two occasions now I have found flies inside the bottle. Is the bottle made from sort insect permeable gortex? Osmotic pressure? Or is there a species of fly able to open the lid, crawl in and close the top afterwards? Are they attracted to the alcohol or the pineapple flavour scent?

Any explaination believed.

Havent a clue but could it be that if you had W/S wash residue around the neck a small wee fly could lay its eggs and tiny maggots have found their way under the cap. These things have a knack of squeezing through the tiniest gap.They soon devolop from maggot to fly. Just a thought!

Topped up from a mucky bottle containing the wee beasties?

A certain specis of fly has apparently evolved to lay its eggs in the washer nozzle jets.

These hatch into larve which wriggle all the way down back into the washer bottle.

Where they then mature.

I am as yet unclear as to the rest of the life cycle.

A certain specis of fly has apparently evolved to lay its eggs in the washer nozzle jets.

These hatch into larve which wriggle all the way down back into the washer bottle.

Where they then mature.

I am as yet unclear as to the rest of the life cycle.

This Larvae issue seems most plausible. Apparently some fly larvae can produce cryoprotectants the most common of which is glycerol which is a longer version of ethylene glycol. No I'm no egg head, I just googled it (sad I know) but if the little blighters can produce anti feeze they can live in places such as washer bottles. We're all doomed! :(