Thread in the valve
A clogged drain line can cause a sewage flood. A big pipe carries waste from your house to the main sewer line under the street. If either of them becomes plugged or overloaded, sewage backs up and flows out of the lowest available drain. That's usually a floor drain. You can prevent a sewage-filled basement or lower level by taking 15 minutes to install a “backwater” valve.
Before you buy a backwater valve, remove your floor drain cover to see if there's already one in place. A call to your city building inspection department is a good idea too. You may learn that sewage backups are unlikely in your neighborhood and that installing a backwater device isn't worth the effort. On the other hand, a backwater valve may be required by your local building code. Some home centers and hardware stores carry backwater valves. Otherwise, call a plumbing supplier or go online. For easier installation, also buy pipe thread sealant that’s formulated for plastic.
Installing a valve in a plastic drain is usually a quick, hassle-free job. But cast iron drains can be frustrating if the threads inside are corroded. If you can't screw in the insert after cleaning with a steel brush, try this: Screw in and then remove a 6-in. long section of 2-in. threaded steel pipe (sold at home centers). The tapered threads on the steel pipe help to clean and straighten the drain threads. If that doesn't work, you can call a plumber to repair the threads with a tap, or you can seal the drain with a 2-in. “test plug” (sold at home centers). A plug will stop rising sewage, but you’ll have to remove it every time you want to use the drain.