Check valve on Aquasafe ro/di

[Popeye]

I have the same ro unit, I have a John Guest switch/tap on the intake before the ro unit and on the outflow after the unit. The flow restrictor stays off.
The only time I open it is for flushing and i just open the intake flow and leave the out flow closed for about 20 minutes. Then turn off both. To make water open the inflow and the outflow taps and bingo.
Hope this helps