Fuel tanker (6)
I believe the answer is:
bowser
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">fuel tanker</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for bowser that I've seen before include "Aviation-fuel tanker" , "Fuel or water tanker" , "vehicle for oil" , "Fuelling tanker" , "Tanker for refuelling aircraft" .)