It carries water in many thousands of drops (5)
I believe the answer is:
drain
'it carries water' is the definition.
The definition suggests a singular noun which matches the answer.
'many thousands of drops' is the wordplay.
I cannot really see how this works, but
'many' could be 'd' (Roman numeral for 500) and 'd' is found in the answer.
'drops' could be 'rain' (drops of water) and 'rain' is found in the answer.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
'in' acts as a link.
Can you help me to learn more?
(Other definitions for drain that I've seen before include "Make weak" , "Filter" , "Remove liquid from" , "Waste pipe" , "Empty of liquid" .)