The answer is silt - I am a member of the new 'Telegraph Clued-up' and one is allowed up to five letter hints for each crossword - using four of those, the answer is confirmed as sift. (Though I do not like the clue either!).
Johndeeby - if you read this, please tell why you refuse to accept what I said above about the answer being confirmed by the Telegraph itself as SIFT - thanks.