The caution against allowing final rinse solutions to come into contact with tanks and reels is, while technically sound, probably irrelevant for at-home, hobbyist users. In a pro-lab setting where there are multiple developing runs a day with potentially rushed/inadequate cleaning of equipment between runs, it's not hard to imagine how residues might eventually accumulate and lead to problems. But for someone using their equipment for only a few runs a month, there shouldn't be any problem doing a final rinse on the reel and in the tank provided he or she washes their equipment in warm water immediately after use.
The primary component in final rinse is surfactant, which is water-soluble and washes off easily. It only becomes a problem if you allow it to dry on the equipment, at which point it can (over many uses) turn into a gummy residue (a good analogy for this is liquid detergent that dries out and accumulates in the dispensing bin of a dishwasher or washing machine). Just rinse it off after each use and you'll be fine. Another good practice is to periodically (e.g., every couple months) wash and scrub tanks, bottles, and reels in a solution of washing soda (sodium carbonate) and warm water. At least, this has been my approach for many years and I've never encountered a problem.
I think a lot of the "no final rinse on reels or in tanks" advice is generated by people who have difficulty loading roll film onto plastic reels, which admittedly can be a frustrating problem. Final rinse residue seems to get frequently blamed for this problem when the likelier culprit is simply unclipped corners at the leading edge of the film getting caught on the various nibs in the reel. (Clipping your film with a corner cutter for paper crafting will eliminate this problem.)
With Jobo tanks and reels, I add enough final rinse to the tank to submerge the film when the tank is on its side, similar to when it's in the processor, and gently rotate it by hand for the requisite amount of time, being sure to reverse direction every 15 or so seconds. The alternate way -- in which you attempt to safely transfer a discombobulated handful of wet roll film from a reel into a container (bowl?) that's specifically designated for final rinse -- always struck me as a bit faffy, but people apparently manage to do it. Wet film is in a pretty delicate state, though, so it's best to limit the amount of time it spends in your hands. For that reason, I've always done the final rinse in the tank. YMMV.
