Impurity remover (6)
I believe the answer is:
filter
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">impurity remover</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 filter that I've seen before include "Remover of impurities" , "Strain" , "Screen out unwanted material" , "Strainer; a traffic light" , "Porous strainer" .)