Cleaner might thump person pontificating there (7)
I believe the answer is:
soapbox
'thump person pontificating there' is the definition.
I can't judge whether this definition defines the answer.
'cleaner might' is the wordplay.
'cleaner' becomes 'soap' (soap is a kind of cleaner).
'might' becomes 'box' (I can't justify this - if you can you should give a lot more credence to this answer).
'soap'+'box'='SOAPBOX'
Can you help me to learn more?
(Other definitions for soapbox that I've seen before include "Crate used for public speaking" , "Make-shift stand for street orator" , "Platform for airing one's views?" , "Makeshift orator's stand" , "Stand on it and declaim" .)