Regularly seen in sauna, vainly is one brawny men hit on (5)
I believe the answer is:
anvil
'one brawny men hit on' is the definition.
'regularly seen in sauna vainly' is the wordplay.
'regularly seen in' indicates alternate letters.
'sauna'+'vainly'='saunavainly'
The alternating letters of 'saunavainly' are 'ANVIL'.
'is' is the link.
(Other definitions for anvil that I've seen before include "part of the ear" , "Forge equipment" , "Metalworker's block" , "On which hot metal is shaped" , "Bone" .)