If you don't use a strong enough screenwash concentrate, you get ths white stuff "grow" in the tank
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As tunnie say, clean the gauze, but also flush the bottle out.
Open bonnet. If PFL/MFL remove grill as well.
Locate pump in bottle - if you have headlight washers, the windscreen pump is smaller of 2.
Pull back rubber cover over top, and unplug electrical connector
Push top of pump towards back of car to unclip from bottle, then lift out
The rubber seal (with integrated gauze) wil likely stay in bottle, gently pull it out, and thoroughly clean
With pump out, pop a hose in washer bottle filler, and flush tank through
If you have headlight washers, worth yanking out that pump using similar method - no gauze on that though, so when the white stuff gets in that, the pump become ineffective
Refit is reverse
Refill, and follow the strength guidance on your preferred screenwash