Drain of energy (3)
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">drain of energy</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 sap that I've seen before include "Undermine the tree juice" , "Imbecile" , "Plant liquid or general vitality" , "Juice; energy" , "Moisture in tree or informal dunce" .)
(Other definitions for exhaust that I've seen before include "Sap - piped emission" , "Completely tire out" , "Weary" , "Waste gas from engine" , "Devitalize, drain of energy" .)