Well,in a bit of a rush, I have swapped over to hydraulic fluid, but due to phone calls etc, not managed to bleed it all out properly yet, but the fluid is now golden coloured, rather than pink/red
When flushing, I first flushed the reservoir, by dropping the return hose off, then ran the engine until fluid stopped coming out of the return (a very short time!). Next I topped the reservoir up with HF and ran it up thinking that should do it, then had a thought and realised the box would basically remain full of ATF, so fitted a small hose to the box bleed nippe and opened it up while I topped up the reservoir until it ran clear, plus turned the steering back and forth a couple of times. The stuff in the reservoir is now clear, if a little foamy. I have left it to settle for a while, and will go back and bleed properly shortly.
Agreed on the ID of the steel pipe, was been rather dim this morning