There is a deviation in place towards the top of the 1st pitch in Diccan, after the rebelays. It has some old damaged rope in situ. I presume the main deviation is further down the shaft ?  And the one at the top is not neccessary (with your own rope/sling)?
CNCC talks about the deviation being further down.  Can anyone confirm?

In times of mega water use both?

The deviation(s) are there to pull the rope away from the worst of the water. In very dry weather it is possible to miss them out altogether, in normal conditions you will want a deviation. It is really your call where you choose to deviate, or whether you choose to get soaked ... we all have our own tolerance level!

The deviation referenced in the CNCC Rigging topo is (by my recollection) is just over half way down the pitch and is very useful to get away from the water (which sprays off a shelf several metres down from the top). I don't remember any deviations nearer to the top of the shaft; just the two rebelays in quick succession against the left wall. However, it is perfectly possible that there are some bits of 'tat' further up that have been used for extra deviations; of course, treat them with appropriate suspicion.

It's been great seeing so many people taking advantage of the dry conditions to visit potholes such as Diccan, Meregill and (my personal favourite) Black Shiver. They show off northern potholing at its finest 

Matt Ewles, CNCC Secretary