If the solenoid adapter is used, remove the 1/4" existing line nut and sleeve, then screw the adapter to the water inlet solenoid. No sealant or Teflon tape is required for solenoid adapter. It is a compression fitting. Tighten the fitting and insert the 3/8" tubing. Leave the ice maker off until the RO system is flushed and full.
This will flush the internal tubing in the ice maker or refrigerator.