Ring up, getting venue for swimming (4)
I believe the answer is:
pool
'venue for swimming' is the definition.
(swimming pool)
'ring up' is the wordplay.
'ring' becomes 'loop' (I've seen this before).
'up' shows that the letters should be reversed in order (in down clue: letters go upwards).
'loop' back-to-front is 'POOL'.
'getting' acts as a link.
(Other definitions for pool that I've seen before include "found in watery location" , "Mere - game" , "Small area of still water" , "Kitty; a billiard game" , "Put in common fund; (pub) game" .)