During a flood, sewage can flow back into your house. Floodwater doesn’t just fill streets and basements. It can also fill sewer or septic systems, causing sewage to “backflow” through drains and into homes. Sewage is a nasty, toxic soup—more damaging, dangerous and disgusting than ordinary floodwater. The lower the drain, the greater the risk—so homes with basements and homes in low-lying areas are the most vulnerable. To find out if this is a likely danger in your home, talk to your neighbors. If they’ve ever had sewage backflow during a flood, your house is probably at risk too. Don’t wait to plan and prepare; home centers sometimes run out of backflow-stopping gear just before a flood.
In some situations, blocking off individual drains is a good approach. In a basement with only a floor drain and a laundry tub, for example, you can stick a test plug in the tub drain and install a “backwater” valve ($8) in the floor drain. But other types of drains are more difficult: The best way to block a toilet drain, for example, is to remove the toilet and plug the pipe. The most reliable way to block a bath or kitchen sink is to remove the trap and cap the drain stub-out pipe. That’s a lot of work.
So instead of fussing with individual drains, consider blocking the main drain line at the cleanout. Most homes have a cleanout near the point where the main line exits the house. Unscrew the cleanout plug, insert a test plug and inflate it with a bicycle pump. This single solution protects your whole house, but has three drawbacks: First, you have to do it immediately when flooding begins and the flow is weak. Strong backflow will make it impossible. Second, any water that seeps into your home (through basement walls, for example) can’t flow out through floor drains. And finally, since your entire drain system is blocked, you can’t use toilets, sinks or tubs. To prevent accidental use, it’s a good idea to shut off the water supply.
The ultimate solution is a whole-house backwater valve installed in the main line. Prices start at about $50 online. Once installed, it protects all your drains without any effort or inconvenience. Installation isn’t tricky but usually requires breaking up the floor—a big, messy job.
1. Protect Floor Drains With a Backwater Valve
A “backwater” valve lets water ﬂow into the drain but not out. To install the type shown above, drop the ball into the drain and screw in the threaded insert. When water rises, the ball seals against the insert. If you have a cast iron ﬂoor drain, the threads inside are probably corroded, so choose a version with a rubber ﬂoat and compression seal instead.
2. Block The Main Line With a Test Plug
The fastest, easiest way to stop sewage backﬂow to all drains is to place an inﬂatable test plug in the main sewer line. Inﬂate the plug with a bicycle pump.