Why are intact coverslips thrown into the waste tray? FAQ Report A:Possibly, the coverslip sensor needs to be cleaned. Ensure that the sensor is functioning correctly. If the coverslip sensor (located between the red suction cups) appears dirty, clean it with a tissue moistened with xylene (work carefully - suction cups must not be immersed in xylene). For a more thorough cleaning job, the sensor can also be removed (details on how to carry out this procedure are available from your Leica service representative). If the problem cannot be remedied through cleaning, you may have to call a Leica service representative to check the system.