How to reach recessed nut to change bottom-entry fill valve

[dmjones500]

I need to replace a broken fill valve, but I can't access the nuts at the rear of the toilet. A flexible hose disappears inside a relatively small hole and I can just see the nut if I shove a camera under there:

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Looking in the top of the toilet, there's nothing that suggests I should be attacking this problem from the top:

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Is there some kind of tool I can purchase to get at this nut? I've got a basin wrench, but it's far too big to fit up the hole. I can just get my fingers up there, but that's about it.

For the record, here's a side view of the flexible hose:

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and from the other side of the toilet, where you can see the copper piping joining to the flexible hose:

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Thanks for any help.

 

[flameport]

Undo and remove the two white plastic nuts (as can be seen in the last two pictures) and lift the cistern up.

If there are any screws fixing the cistern to the wall, they will need to be removed as well.

 

[dmjones500]

Brilliant, thanks! I knew there must be a simple answer, not sure why I didn't spot those already!