At a high level, the
tanks break down into
three main categories:
1.
AFS - The oldest style, a 'universal'
tank which fits many mods.
2.
AVS - The middle version, it's an aluminum tank which is made for a 901/808 and sits atop the GGTS control tank (an overflow tank).
3.
UFS - The current version (with clear window), sometimes confusingly called the AVS v.3. It's stainless steel and has a clear window and comes with its own control tank and (to my knowledge) only works on the GGTS.
So... to answer your question, the
AVS Center Post on the COV site is for #2 above. That part is not on the UFS that I can see.
I'm not sure if all of that is 100% correct, but it's probably enough to answer your question. Here's a
link to the GG Wiki.