Swimmer's breathing tube (7)
I believe the answer is:
snorkel
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">swimmer's breathing tube</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for snorkel that I've seen before include "diving equipment?" , "Tube supplying air to swimmer" , "Breathing aid for a swimmer" , "Breathing tube for under-water swimmer" , "tube at sea" .)