Ron's returned a man's breathing tube (7)
I believe the answer is:
snorkel
'breathing tube' is the definition.
(I've seen this in another clue)
'ron's returned a man's' is the wordplay.
'returned' is a reversal indicator.
'a man' becomes 'kel' (I can't explain this - if you can you should give a lot more credence to this answer).
'rons' in reverse letter order is 'snor'.
'snor'+'kel'='SNORKEL'
Can you help me to learn more?
(Other definitions for snorkel that I've seen before include "Diver's breathing tube" , "Tube supplying air to swimmer" , "Breathing tube for under-water swimmer" , "Surface breathing tube" , "Breathing aid for a swimmer" .)