BMW 3series tourer,Windscreen washers jets not working! ?

When I ask for the windscreen washers to clean the windscreen the nozzles only send a dribble of water out. I think there must be a blockage from the reservoir, which is full, to the windscreen nozzles, the pump works ok and the rear wash is fine, it is the lack of pressure on the front nozzles that I need to sort out is there a filter somewhere?.