Hi
I just sorted my rear washer. Remove the interior panel over the motor, pull off the water pipe and test the wash wipe. Still no water so removed the one way valve, retest and water shooting out. Dismantled the one way valve carefully by depressing the two plastic tabs and removing the rubber Hemilich valve thingy and cleaned then was obvious that the two small holes on the outside of the inner sleeve were blocked with sludge (easier to see for real then describe but its all pretty obvious), put everything back together and works perfectly.
As an aside my father who was a vehicle evaluation enginner for rover and landrover when testing in cold climates such as Minnesota said they would routinely remove the one way valves so that the wash solution would sink back to the reservoir and be less likely to freeze. Obviously you then have to wait for the pump to fill the pipes all the while watching your rear wiper scrape the dirt across the glass behind! Not ideal.
Just have to remove both bumpers to sort the parking sensors and have a chat to the reversing camera so see why it sulks so much and only works one in twenty times or so.
Tom