The most common and most likely answer to this crossword clue is the 8 letter word CISTERNS
I've seen this crossword clue in Independent
C
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S
T
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Buddy explains!
The straight part
We know that "Tanks" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case tanks = cisterns.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does CISTERNS mean?
CISTERNS noun- A reservoir or tank for holding water, especially for catching and holding rainwater for later use.
- In a flush toilet, the container in which the water used for flushing is held; a toilet tank.
- A cisterna.
- The vessel surrounding the condenser in a steam engine.