Vessel containing one last bit of pale amber liquid (5)
I believe the answer is:
urine
'amber liquid' is the definition.
(urine might be amber in colour)
'vessel containing one last bit of pale' is the wordplay.
'vessel' becomes 'urn' (urn is a kind of vessel).
'containing' is an insertion indicator.
'one' becomes 'i' (Roman numeral).
'last bit of' suggests the final letters.
The last letter of 'pale' is 'e'.
'urn' enclosing 'i' is 'urin'.
'urin'+'e'='URINE'
(Other definitions for urine that I've seen before include "Stuff that's passed" , "Water that one passes" , "Waste product" , "Wee" .)