I agree with rob about the possible cause and to drain washer bottle if possible, if the washer bottle is the type that inaccessible i.e. inside the wing, place a hose pipe in the neck as far as poss. and turn on the tap to expel as much water as poss. Once it's running semi clean, either drain bottle if poss. or use the washers to empty some of the contents. I would not use Oxi-Clean or similar as I not sure what effect it would have on seals in the pump etc and would refrain from over prolonged use of washers as this may burn out pump. Once system is reasonably clean, top with at least 50/50 ratio of screen cleaner and fresh water.