Cleans up occasional leaks spreading around 'below' (8)
I believe the answer is:
launders
'cleans' is the definition.
(laundering is a kind of cleaning)
'up occasional leaks spreading around below' is the wordplay.
'up occasional leaks spreading' becomes 'las' (I can't justify this - if you can you should give a lot more credence to this answer).
'around' is an insertion indicator.
'below' becomes 'under' (synonyms).
'las' enclosing 'under' is 'LAUNDERS'.
Can you help me to learn more?
(Another definition for launders that I've seen is " Washes and irons".)