It rains, empty sewage at sea, this might get dirt on surface (9)

I believe the answer is:

sanitiser

I'm a little stuck... Click here to teach me more about this clue!

'might get dirt on surface' is the definition.
I don't know anything about this answer so I can't judge whether it can be defined by this definition.

'it rains empty sewage at sea' is the wordplay.
'empty' says to hollow out the word (remove centre letters).
'at sea' is an anagram indicator.
'sewage' with its middle removed is 'se'.
'it'+'rains'+'se'='itrainsse'
'itrainsse' is an anagram of 'SANITISER'.

'this' acts as a link.

Can you help me to learn more?

(Another definition for sanitiser that I've seen is " One making (something) clinically clean".)

I've seen this clue in The Guardian.

Want a hint initially instead of a full solution? Install my app