Eh, my guess is that Varram is looking for a mask, and is doing so by trying to use Diderius's pool. I'm not sure we've had any hint that the mask is actually here. That's the main reason I want to use the pool. We might be able to learn more about who is at the head of these cults uniting at the well, and/or find out the locations of the masks. Would be nice to use it without naga / Yaun-ti coming to kill us like they did Varram's group.
Daishain, I assume we've moved into the room a bit further to speak to the Highest? How close are we to the leader now?
We also don't know how the naga/yuanti feel about Diderius. Maybe the Naga/Yuanti don't like Diderius? We can attempt to bring up the idea of dealing with him in exchange for safe passage rather than pay the 10k price tag. That could potentially kill two snakes with one stone.