Relation with a rarely empty storehouse (7)
I believe the answer is:
granary
'storehouse' is the definition.
(granary is a kind of storehouse)
'relation with a rarely empty' is the wordplay.
'relation' becomes 'gran' (I've seen this before**).
'with' is a charade indicator (letters next to each other).
'empty' means to remove the middle letters.
'rarely' with its middle removed is 'ry'.
'gran'+'a'+'ry'='GRANARY'
(Other definitions for granary that I've seen before include "Harvest store" , "barn" , "Agricultural storehouse" , "Grain storehouse" , "breadbasket" .)