Drains away nitrogen inside, showing guts (7)
I believe the answer is:
innards
'guts' is the definition.
(I've seen this before)
'drains away nitrogen inside' is the wordplay.
'away' indicates an anagram (letters move away from their original places).
'nitrogen' becomes 'N' (N is the chemical symbol for nitrogen).
'inside' is an insertion indicator.
'drains' anagrammed gives 'inards'.
'inards' placed around 'n' is 'INNARDS'.
'showing' acts as a link.
(Other definitions for innards that I've seen before include "Most of haggis" , "Insides" , "Informally, stomach and bowels" , "Internal organs" , "Works" .)