How much fluid does it take to fill a rear Hope E4? If I want to completely replace the fluid how much do i need to put through?

The standard Shimano kit contains 50ml and is always more than enough

Cant be more than ~5ml. But if you’re bleeding an old brake I like to use more than needed to flush the old fluid out thoroughly. Normally put enough into my shimanos that fluid goes from black and bleugh to red like it should be.

At best 20ml an end, including res I reckon.