Remove quietly from drain (6)
I believe the answer is:
delete
'remove' is the definition.
(deleting is a kind of removing)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for delete that I've seen before include "'Cancel, cut (6)'" , "Rub out, expunge" , "Erase or destroy" , "Take out" , "Wipe out" .)