If the drain you are talking about is the drain in your concrete floor then what you need is a backflow preventer. Your local hardware store should have them for about $20.00
This gadget allows water (if you have a flood) to flow into the drain but at the same time it prevents any sewer debris or "aroma" from entering your home. When you go to the store, first measure the inside diameter of the drain opening. That way you'll pick up the correct sized gadget.