I had success in sorting the probem but i'm still not really aware of what was causing it.
I removed the nearside wheel.
removed the six screws that hold in the liner. All are visible apart from one under the sill.
Removed one bolt in the engine compartment and two underneath the wing that holds the reservoir in place.
Pulled out the filler section of pipe. A few twists and pulls remove this.
Dropped the water bottle enough to remove the feed pipes off, drained the bottle and removed the motor.
The bottom of the bottle was full of gunge so I prised out the black filter and cleaned it and the bottle.
Tried everything again and still no flow to rear.
I tried blowing in the pipe and there was obviously a blockage.
There is no signs of a non return valve.
I blew in compssed air and still blocked.
I then filled a funnel with hot water and suspended it for a few minutes. More compressed air and left attached with 40psi for five minutes. Still no joy.
I then stuck a piece of insulated wire up the pipe for the 18 or so inches that it would go and it appeared to go no further than where the pipe disappears into the front bulkhead. I repeated the compressed air and finally signs of some water were detected on the rear window.
I left air flowing for a few more minutes then put the pump and pipes all together and after a minute of depressing the rear wipe switch, it was working again.
There was no sign of any dirt, so I can only assume that there may well be an NRV hidden somewhere.
I cannot think of any other reason for a solid blockage.
Nobby, December 2008