Spam fan was regularly back in bog (5)
I believe the answer is:
swamp
'bog' is the definition.
(I've seen this before)
'spam fan was regularly back' is the wordplay.
'regularly' indicates alternate letters (regularly take one letter, leave next etc.).
'back' shows that the letters should be reversed in order.
'spam'+'fan'+'was'='spamfanwas'
The alternating letters of 'spamfanwas' are 'pmaws'.
'pmaws' reversed gives 'SWAMP'.
'in' is the link.
(Other definitions for swamp that I've seen before include "Slough" , "Seasonally flooded lowland" , "Marshy land" , "Boggy area" , "In flood" .)