Your latest photo is obviously (I hope!) The Canal in Dan yr Ogof. Unless you've taken your own inner tubes into somewhere else, of course!
As for your previous photo, I've been in the Waterfall Series but not to The Annex so haven't seen the formation myself. But when no one had put forward a guess for a while, I decided to pull my finger out and follow your clues. OFD, ok. "Described as 'fine black gour pools'. Right, that must be from a description - not much gets passed me! You being a student and therefore young, it has to be a description on this here interweb thing. So I started reading Brendan Marris' description of OFD, which being such a big cave, is very long. I started with OFD 1 but ran out of time just as I started on the Waterfall Series! The Annex and the black gour pools are described at the end of that section. I was a few minutes reading away from the answer. 🙁
, yeah it really just an after thought at the end of the description that one sentence. I almost didn't go through the squeeze to get there cause I got my legs in and realised how nasty it would be to get back out but decided to commit anyway. 
