Remove old bug climbing in drain (9)
I believe the answer is:
extirpate
'remove' is the definition.
(I've seen this before)
'old bug climbing in drain' is the wordplay.
'old' becomes 'ex' (prefix meaning former or onetime).
'bug climbing' becomes 'pat' (I can't justify this - if you can you should give a lot more credence to this answer).
'in' indicates putting letters inside.
'drain' becomes 'tire' (tiring is a kind of draining).
'pat' placed into 'tire' is 'tirpate'.
'ex'+'tirpate'='EXTIRPATE'
Can you help me to learn more?
(Other definitions for extirpate that I've seen before include "Remove completely" , "Destroy totally" , "Completely destroy" , "destroy utterly" , "Root out" .)