Technical Windscreen washer system

[centomental]

Is there a filter in the washer bottle which may clog? My washers only produce a trickle of screenwash. Cleaned nozzles, slight difference but still very weak.
Flow from nozzle pipe weak. Pump motor sounds healthy (loud). How can I check pump?

 

[David C]

There are non return valves in the lines which fail.
I remember replacing those on mine.