Quick question...

[Chalked]

I normally do that but less options on plastic... pretty sure it's 8mm grey plastic

Oops . Should have read the posts better!

Plastic, not copper.

 

[mfgs]

You sure it's 8mm plastic and not 10mm? Don't think I've ever seen 8mm plastic, is that a thing?
I hate those collapsable reducers bloomin horrible idea, I'd be 'too busy' unless there's scope to redo all the pipe ends, if the pipes come up from under the floor you're laughing.

Good point, I have only seen 10mm plastic too.