sieve

• sieve [countable]
• 1
• a) a round wire kitchen tool with a lot of small holes, used for separating solid food from liquid or small pieces of food from large pieces
• b) a round wire tool for separating small objects from large objects
• 2

   have a memory like a sieve

  informal to forget things easily

Definition from the Longman Dictionary of Contemporary English
Advanced Learner's Dictionary.