Does the warning light for the washer fluid come on pretty early? Mine started telling me it needed refilling about 2 weeks ago now and its still going.
It depends on weather you have headlamp washers. The warning (if fitted, because it is only fitted with the optional 'Winter Pack'

) usually comes on when the bottle is about three quarters empty. What then happens - it sort of goes into a 'washer fluid preservation mode'. The headlamp washers will first stop working, then the rear screen p!sser, and the front screen washers will only stop when the bottle is completely empty.
I'm wanting to wait till its pretty much bone dry to then wash it out as above.
It all depends on what washer fluid you have used - because as Mr Lapou correctly pointed out, mixing certain different kinds of washer fluid can actually cause it to form 'jelly' like substances in the bottle, and will seriously clog fan jets, especially if they are heated. The cheaper, poor quality washer fluids tend to be made of methanol - which is just the proper name for the primary agent in methylated spirits (meths). Whereas the better quality fluids (including the genuine VAG, and the VCP stuff from Lidl) use the higher quality ethanol, which is pure alcohol <hic, hic, hic

>. And just like engine oils, washer fluids also have 'additives' in them too.
So, if you are damned not to use the genuine VW stuff all the time, try at least to use one which is ethanol based, rather than methanol. Good luck in finding some though, because the vast majority of screen wash fluids are still based on methanol. A good tip is to check the frost protection - the genuine VAG and Lidl fluids go down to minus 70degC - whereas the methanol ones only go down to minus 20, minus 30 if you are lucky.
HTH