With all due respect I dont think that removing the rads and carrying
them out is the easiest way to flush a sealed system. If the system
was properly designed, (yes I know the OP called it a dogs breakfast)
the fill point and drain point should be on opposite sides. (i.e. one
on the hot flow from boiler, one on cold return). Then you can

switch off, release pressure at the release point.

connect fill and drain hoses, open drain valve, close pressure
release valve.

Turn on supply. Then by opening and shutting valves round the house,
you can send a fast stream of water through each rad in turn. This
should remove a lot of the sludge except if a rad is solidly blocked;
if so, then you will have to remove that rad and flush it.

Refill as normal adding Fernox or similar sludge-remover. Repressurise,
run hot for a while as per instructions.

drain, flush, refill adding anti-rust.

If the drain point is on the wrong side of the system, you will need
to cut pipe and insert an extra drain point. You may prefer to remove
rads.

If you do decide to remove and flush out rads, note:
1. When you undo the joint, water will ooze out. When you definitely
separate the pipes, it will gush.
2. However carefully you tilt a rad to drain it, there is always a
little bit of mucky water lurking inside, waiting for a chance to run
out & ruin your carpet. Carry rads upside down, with ends plugged.

Making joints. I know that other posters use PTFE tape, I have had
better results with Fernox leak sealer (I have no connection with
Fernox). It comes in a toothpaste tube, you smear it onto the male
part of the joint, dont get it on your hands, bad for skin.