Cleaned my own windows yesterday and could not work out why the first few were left with spots.
My 12 year old did the last few and they are perfect, but the first few were awful.
I realised I had used two brushes that had been in the van for a weekk, unused, and concluded that the brushes must be dusty and therefore need cleaning regurlarly.
How do you keep yours clean?
Dunk in a bucket of pure and gg3?