In article .uk,
Ed Sirett writes:

I disagree that the best practice is to disconnect the loop, but that's
what our lords and masters require, eh. A small quantity of water
dribbles out of the loop after disconnection (OK so you can use a cloth to
catch it). Also a small amount of air is introduced into the system when

Yes. I connect up the supply end first and very loosely connect
the heating end, turn on the water so it blows most of the air
out of the loose connection, before tightening it up to force
the water through to the heating system.

it's reused. Also dust caps are not supplied with most filling
loops so these have either to be supplied or the possibility of 'foreign'
matter getting in has to be endured.

or of young enquiring minds thinking
"what happens if I turn this knob?" ;-)

Mine's in a rather shallow cupboard, and the door won't stay shut
if the filling loop is left connected anyway.

--
Andrew Gabriel