Block-It-Out, a Drain Cover (IMAGE) Nanyang Technological University Caption Block-It-Out is an innovative swivelling drain cover which allows water through, but can block out mosquitos from entering to breed, helping to prevent the spread of dengue. Credit NTU Usage Restrictions For this story only License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.