You and I have sat around as one does in a sauna (5)
I believe the answer is:
sweat
'one does in a sauna' is the definition.
I can't judge whether this definition defines the answer.
'you and i have sat around' is the wordplay.
'you and i have' becomes 'we' (I can't justify this - if you can you should believe this answer much more).
'around' is an insertion indicator.
'we' inserted into 'sat' is 'SWEAT'.
'as' is the link.
Can you help me to learn more?
(Other definitions for sweat that I've seen before include "Salty fluid secreted by glands" , "Waste (anag.)" , "Male perspiration?" , "Soldier" , "Perspire" .)