Old hair felt by the looks of it, if so it doesn't contain asbestos.
The one you linked to earlier, https://www.screwfix.com/p/floplast-solvent-weld-reducing-coupler-55-x-43mm-white/65568, will fit in the 50mm tee...
https://www.theunderfloorheatingstore.com/media/ufhs/manuals/Cyclone-Heat-Pump-2016.pdf, page 31
Edit - that link wont open for some reason but...
Yes, get a good quality one such as McAlpine.
Not if fitted properly, never had a problem with them.
That won't fit into clay.
Yes, it compresses the washer onto the pan
No, after the clamping plate, as per your picture.
The picture is correct, washer between pan and cistern.
It should be clamped and compressed to stop water leaking when flushed https://www.toolstation.com/close-coupling-doughnut-washer/p39353
Does the handle pull off to reveal anything?
Is this it? https://www.showerspares.com/downloads/triton_aquatronic_1_aquatronic_1.pdf
No, except the donut washer which fits between the cistern and pan.
I think we all agree it is a poor job and needs redone. I'm not sure what other advice you need.
They are slightly adjustable, or not pushed fully home when fitting, sounds like you just need two the same.
You could get a couple of these, https://www.toolstation.com/rigid-radiator-valve-extension/p13659, and cut them down.
Cut it flush with the wall and fit a Multikwik extension "A". You can then cut this to the correct length and fit a normal wc connector.
No problem, neither am I. I was only trying to explain what the instructions meant, but I agree they are not always sensible on site.
Happy to be...
They are normally full size units and that door looks like 600mm. You would normally fit the corner unit then the corner post then a full unit...
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