I'm guessing the flush valve you have is a Wirquin, the button hole is huge compared to pretty much all the others, once you've drilled the hole you're stuck with using Wirquin valves unless you replace the panel that you drilled.
The Wirquin valves are good but I wouldn't choose them just...
Yeah it depends what fitting is on the end of the flexis you have. If it's nut and olive then straight onto copper, if it's tap conns with rubber seals then a 15mm - 1/2' union would be the preferred choice but people do attach them to standarrd compression fittings like couplers or ISOs...
Offer your new tap up and see where the flexis dangle to. Cut a piece of 15mm copper for each feed and connect them to the tees, attach the flexi to the copper you just put in.
You will probably need an extra nut and olive for the top of those compression tees as the flexis are connected to...
If the water was drained down for an extended period before you moved in the copper pipes will oxidise and you will get some discoloration until the particles of oxide have been flushed out.
That looks excessive though, a house I recently worked on had some greeny/blue marks running down the...
He posted the pic, I managed to see it but had to fiddle with the URL.
View: https://*********/bDliMKk
1588361465
My guess is the dome parts unscrew to reveal the screw that holds the rest on.
With some cc toilets you can change the inlet valve without separating the pan and cistern, you may be lucky. Give us a picture from underneath where the cold water pipe connects to the bottom of the fill valve.
If you haven't already bought the fill valve, it looks like only a few will fit in...
Is 21mm the internal or external diameter of your pipe?
I have in the past used a short section of 22mm copper tube and 2 jubilee clips to join two w/m hoses together and it was a tight fit but went on without needing to be heated up. The hose then attached to a standard spigot.
If the internal...
If your pipe diameters are a couple of mm different you probably have a combination of push fit pipe and solvent weld.
Use a multifit coupler or elbow from McAlpine to connect them.
I thought the thin ones were for ceilings only, got some about that thickness on my bathroom ceiling, caught one really lightly with the drill and chipped it.
Wouldn't have it on the walls if it's the stuff I'm thinking about - 250mm wide.