In article , dave @ stejonda
writes

Now draining the CH system after having Fernox Restorer running around
in it for a few days.

Filling and draining it until the water comes out is clear is
'interesting work' - running up and down stairs | loft ladder | opening
radiator bleed points | bleeding rad's...

How clear do I really need to get the water before it's clean enough?

Not answering your question directly, but can you flush it through rather
than filling and draining? Hose connected to a drain point near the boiler &
fill continuously via the filling point or header tank. Close radiators off in
selected areas to force flow through distant rads.

My system was designed to make this possible, with an isolation valve in
the boiler feed, but you may be able to stop reverse flow through the boiler
(except when you want to flush that loop) by closing the pump isolation
valves (if fitted).

I flushed through for 30mins, closing off selected rads/areas to make sure
everything was flushed, water was totally clear at finish. No need to bleed
when flushing if you don't drain first.
--
fred