Get a mate to hold the pumps when you press the washer button on the steering . If like me you have a two pump set up on the washer bottle you can then tell if its the front or rear one. If both of them buzz when you press their button, the you need a new non return valve which costs about £2-3 . You can test the pipe and the outlet nozzle is clear or working by blowing down the pipe one the non return valve is removed. If you can blow through it and air comes out of the nozzle then you have the culprit. I did mine by adding a new length of 2 metre pipe, a new non return valve, new pump and new LR nozzle too. Overkill but cheap at about £15 for it all.
I have nice MOT standard washer jets now...