IMO The black o-ring fits the interior part of the chimney so I put it there matching the way the white/clear ones that were preinstalled in the other two chimneys. Still begs the question WHY did they omit doing it for the Atlantis chimney? And how is the black silicone DIFFERENT the the white, I'll bet the white is perhaps more heat RESISTANT, and the black ones could represent a problem, something to keep an eye on. My online texting with Eciggity customer service was a dead end!
I got my reply from Eciggity a little bit ago and they said the black o-ring goes in the chimney. Nothing more. No answer to the reasoning it wasn't white like the others or pre-installed like the others. It does seem to work and no odd tastes yet.