Club he joined to go swimming (5)
I believe the answer is:
bathe
'go swimming' is the definition.
(I've seen this in another clue)
'club he joined' is the wordplay.
'club' becomes 'bat' (as in sporting equipment).
'joined' is a charade indicator (letters next to each other).
'bat'+'he'='BATHE'
'to' is the link.
(Other definitions for bathe that I've seen before include "Become immersed in" , "Swim or paddle" , "Wash, soak" , "Wash in water" , "Suffuse" .)