Instructions on mine read to flush till black carbon stops coming out. I continue to flush a few glass fulls until I am certain water is perfectly clear. If it has been unused for a few days then I flush a gallon or so through again.
My Brita pitcher says to soak and then flush the filter cartridge.
2017 SLX 195RB
2014 Jeep Grand Cherokee Overland, gas 3.7 V6
Andersen WDH hitch
Dometic Milenco Aero mirrors