Single out the cold water pipe with the hole in it (6)
I believe the answer is:
Here is my best explanation:
'single out' is the definition.
'the cold water pipe with the hole in it' is the subsidiary indication.
'the cold' becomes 'c'.
'water pipe' becomes 'hose' (I've seen this before).
'with' says to put letters next to each other.
'the hole' becomes 'o'.
'in it' means one lot of letters goes inside another.
'chose' enclosing 'o' is 'choose'.
(Other definitions for choose that I've seen before include "Opt", "Elect", "Pick, select.", "So echo (anag) - wish", "Vote", "Select, opt for", "Select, pick" and "Think fit".)