Front washer works fine but rear washer is doing the triple pump on activation but only a little water is dribbling out from rear nozzles but water bubbles out of the front reservoir tank. I have tried cleaning nozzles but it has made no difference. Any ideas?

Try pulling the inner plastic trim - gently - off the inner top of the tail gate - it's held on by plastic 'tongues' moulded into the rear of the plastic. You will be able to see the black rubber tube that feeds the jet - it goes to a black plastic moulding on the motor boss. Pull ithe tube off carefully and try the pump again. If you get a good flow let it run a few presses and se if it pushes any crap through the system, like green gunk.

No flow, you could try the one way valve in the tubing further along.

However, it's normally blocked in the jet itself. Do a search on here, the jet blocking and filling the rear wiper motor with water is a common defect, eventually it bloggers the motor etc.

I have had to change 2 non return valves (NRV) on my fattie. It's easy to check. As stated above, take cover off, pull pipe from valve and check flow before and after the NRV. If the flow is fine after the NRV then it must be the wiper jet that is blocked. Remember to put a bowl or bucket it the car to catch the water when testing.  Previously..
Vogue SE TD6
Defender 90 2.4
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Vogue 3.5 EFI