Abstract: A retrofittable drain insert for existing bell shaped traps and other type drains is provided. The drain insert enables an existing bell trap or pipe drain to be modified and upgraded easily by not only preventing the backflow of sewer gases but also by substantially reducing the backflow of fluid through the drain into the drained area. The drain insert includes a housing with a valve means suspended by an expandable suspension means which easily fits into and can be mounted within the existing drain opening. The valve means has a larger diameter than the housing so as to form a gas tight and fluid tight seal, however, it has a smaller diameter than the existing drain opening so as easily to be retrofittable and fit therein.