Thanks to your replies, I now have a clear understanding. When I disconnected the yellow waste water line from the connector, I saw that there is a restrictor ALREADY in place. (The blue 'plug side' of the restrictor is just showing at the end of the yellow waste line; the 1mm black tube of the restrictor is inside the yellow line. Trailing its tail downstream, so to speak.) The flow restrictor taped to the outside of the bag with the RO membrane turns out to be an EXTRA one, supplied by AquaFX. Cool. I suppose they wanted to make sure that if the originally-installed one became plugged up, I'd have an extra one on-hand, to tide me over til I could order another spare. Very nice. This also must be why there was no mention of how to install it when I read the manuals: it was pre-installed!
I guess that this is one of the reasons why so many I've spoke to recommend AquaFX (one of our sponsors) so highly.
Thanks again for the help! ..Karl