I assume people are referring to non-corroding, nice bendy copper nickel alloy or cunifer pipes, rather than pure copper?
I've always understood that pure copper is not suitable for ABS applications and is banned in some countries including Australia. But I've never found an authoritative document confirming either of these much repeated 'facts'. I know people on here have regularly said they fitted copper, does anybody have technical or legal source confirming the suitability of pure copper pipes for ABS?