So I eventually got round to following the guide I linked earlier and all went well, but not the result I wanted.
A few things to note that isn't mentioned in the guides;
- the smaller pipe will most likely need stretching/loosening to slip on to the return pipe easier. I done this by squeezing in two screwdrivers and rotating them in opposite directions
- make the hole in the bottle top big, I was niave and thought about 8mm was enough which wasn't enough to let the fluid flow through fast enough
- make sure you have paper towel to clear spillage as you will inevitably spill some when pulling the pipes off
So now the fluid is flushed and at a sensible level, it is still grinding and making noises. Because I didn't make the hole big enough it did not get enough fluid through and caused the steering to go very hard. I've topped up a lot more fluid and now it's easy to move the wheel but it grinds. It also grinds when not moving the wheel. Is this the pump screwed and need replacing or do I need to leave this running longer to get air through the system or should I add more fluid until it's over the limit and drain after? In total I've left it running about 5 mins to hopefully clear it, and it is no longer bubbling
Video of the noise...