James Amor wrote:

As I was installing my new towel rail a question dawned on me.... how do you
drain it down after it is full? It is connected to the C/H system via two
vertically mounted straight through valves, so the usual 'break the union
with a tray underneath' method is out of the window.

The only two options I've though of a
(1) Drain the system down until the rad is empty (lots of hassle)
(2) Unscrew the bleed valve assembly from the top and then use a hose to
siphon out most of the water, before unscrewing one union with a BIG sponge
handy (feels like a bodge.... with the bonus of getting a mouthful of
fernox!).

(3) put the tray underneath, crack the joint and try to position the
tray to catch the jet of water; wrapping a cloth around the joint/pipe
leading down into the tray as a conduit for the water - messy.

(4) just DON'T.

David