Drains in Sweden well up (4)
I believe the answer is:
saps
'drains' is the definition.
(sapping is a kind of draining)
'sweden well up' is the wordplay.
'sweden' becomes 's'.
'well' becomes 'spa' (I've seen this before).
'up' says the letters should be written in reverse (in down clue: letters go upwards).
'spa' reversed gives 'aps'.
's'+'aps'='SAPS'
'in' is the link.
(Other definitions for saps that I've seen before include "Drains energy from" , "Pass around foolish people" , "Coshes" , "More than one fool" , "mugs" .)