Though I've solved this i thought i'd post what I did to fix it.
This has bugged me for ages as it has not worked ever since I've had the car.
First I pulled the black nozzle with 2 holes in it off cleaned that as it was blocked.
Took the inside trim off the hatch back then pulled the rubber hose off and checked water was coming out of that and it was.
Then I took the white thing off that the rubber hose plugs into (this was completely blocked) washed in hot water using thin wire to pierce through the crud and clean it so I could blow through it with ease.
Then I used a wire to put in the outlet hole that feeds right through to where the white thing plugs into (this was also completely blocked)
Tools used:
Pliers
Torx screwdriver to take inner trim off
Wire (I used the wire from one of those black ties that electrical item cables come tied with)
Outcome was great so powerful though I had to adjust the output jet angles to point at the rear window as it was traveling a good few meters in the direction the wiper was aiming at!
I hope this helps some one that is bugged by not being able to clean your rear window on the motorway or in the country lanes like it did me.
This has bugged me for ages as it has not worked ever since I've had the car.
First I pulled the black nozzle with 2 holes in it off cleaned that as it was blocked.
Took the inside trim off the hatch back then pulled the rubber hose off and checked water was coming out of that and it was.

Then I took the white thing off that the rubber hose plugs into (this was completely blocked) washed in hot water using thin wire to pierce through the crud and clean it so I could blow through it with ease.

Then I used a wire to put in the outlet hole that feeds right through to where the white thing plugs into (this was also completely blocked)

Tools used:
Pliers
Torx screwdriver to take inner trim off
Wire (I used the wire from one of those black ties that electrical item cables come tied with)
Outcome was great so powerful though I had to adjust the output jet angles to point at the rear window as it was traveling a good few meters in the direction the wiper was aiming at!
I hope this helps some one that is bugged by not being able to clean your rear window on the motorway or in the country lanes like it did me.