On mine (Rockwood 8289ws), the "restrictor" is a separate piece from the threaded fitting, and pops right out. I can see in the above picture that this one is slightly different than mine, but still looks like it may be a separate piece (slightly different color)?
On our last 2 trips I did have a low pressure/flow problem. The first time I just assumed it was the campgrounds supply, but when it happened again I investigated and tried removing the restrictor. It did help. I still plan on the Oxygenics.
'04 GMC Sierra 2500HD, CCSB, D/A, MaxBrake, B&W Companion, Retrax Pro, AR Power Steps
2013 Rockwood 8289WS w/Diamond pkg
1969 Camaro RS/SS Convertible
Dad's old 1968 Empi Imp (recently recovered from under 21 years worth of boxes/dust)