Not just the congealed stuff, all kinds of dirt. I thought about fitting something over the pump outlet where it extends into the bottle but that's not too practical to actually get at. Although bits of congealed stuff can break off and travel about.
Washer jets (the later 'atomising' type ones especially) are a royal pain to clean out, sometimes even with compressed air they do not work very well. Yes, you can fit these to older vehicles without cutting your bonnet
I just thought about those cheap plastic inline fuel filters (the clear ones) intended as generic replacements for carb engines.
I wonder if fitting one of those into the actual washer line, just say an inch or three after said pipe exits the pump would be an idea ?
I cannot see it restricting flow / pressure much, but you never know.
Any thoughts ?