Corrosive drops in a Channel Islands sewer? (4,4)

I believe the answer is:

acid rain

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'corrosive drops' is the definition.
'acid rain' can be an answer for 'drops' (I have seen 'Harmful drops' mean 'acid rain' so perhaps 'drops' could also mean 'acid rain'). I am unsure of the 'corrosive' bit.

'a channel islands sewer?' is the wordplay.
'channel islands' becomes 'CI'.
'sewer?' becomes 'drain' (drain can mean a sewer).
'a'+'ci'+'drain'='ACID-RAIN'

'in' is the link.

Can you help me to learn more?

(Other definitions for acid rain that I've seen before include "Form of pollution" , "Devastating drop" , "Type of pollution" , "pollution falling" , "Harmful atmospheric fallout" .)

I've seen this clue in The Sun.

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