Model train in state that's healthy (8)
I believe the answer is:
sanitary
'healthy' is the definition.
(thesaurus)
'model train in state' is the wordplay.
'model' is an anagram indicator.
'in' is an insertion indicator.
'state' becomes 'say' ('say' can be a synonym of 'state'**).
'train' anagrammed gives 'nitar'.
'nitar' put into 'say' is 'SANITARY'.
'that's' acts as a link.
(Other definitions for sanitary that I've seen before include "Hygienic and clean" , "Free from dirt or infective matter" , "Relating to health" , "Relating to hygiene" , "Any sitar (anag.)" .)