Go wild, rent toilets on horseback (3,5)
I believe the answer is:
let loose
'go wild' is the definition.
(I've seen this in another clue)
'rent toilets on horseback' is the wordplay.
'rent' becomes 'let' (I've seen this in another clue).
'toilets on horseback' becomes 'loose' (I can't explain this - if you can you should believe this answer much more).
'let'+'loose'='LET LOOSE'
Can you help me to learn more?
(Other definitions for let loose that I've seen before include "Set free, release" , "Set free from restraint" , "Release, remove restraints" .)