I rant madly, trapped in the French toilet (7)
I believe the answer is:
latrine
'toilet' is the definition.
(latrine is a kind of toilet)
'i rant madly trapped in the french' is the wordplay.
'madly' is an anagram indicator.
'trapped in' is an insertion indicator.
'the french' becomes 'le'.
'i'+'rant'='irant'
'irant' with letters rearranged gives 'atrin'.
'atrin' inserted into 'le' is 'LATRINE'.
(Other definitions for latrine that I've seen before include "Primitive toilet" , "Camp lavatory" , "public toilet" , "Lavatory (in barracks)" , "A military lavatory" .)