Men certainly trampled interior (7)

I believe the answer is:

latrine

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'interior' is the definition.
Although both the answer and definition are singular nouns, I can't understand how they can define each other.

I can't explain the rest of the clue.

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(Other definitions for latrine that I've seen before include "public toilet" , "Reliant on military loo" , "waste disposal unit" , "office" , "Military convenience - reliant (anag)" .)

I've seen this clue in the Sydney Morning Herald.

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