If you live in an area prone to flooding or heavy rain, you should be prepared to plug your drains to prevent sewer backup.

“Raw sewage not only can damage building components and carpeting, it also has high concentrations of bacteria, protozoans and other pathogens that can pose serious health risks,” says Carl Pedersen, North Dakota State University Extension Service energy educator.

Deciding if and when you should plug your drains depends on a variety of factors. For example, you should plug all drains in the lower levels of your home when local officials warn residents to do so or if you plan to evacuate because of the potential for flooding.

“But do not wait until flooding is imminent to attempt to obtain plugs because they may not be available, or there may be situations that need special attention in your home,” Pedersen says.

You may not need to plug drains because many new homes have anti-backflow or backwater check valves in the main sewer line that reduce the potential for sewage backup. While these valves are designed to stop backflow, some have failed, so you must decide if you want the added protection of plugging drains.

Pedersen recommends you inspect your check valves annually to make sure they are free of debris and working properly. If your home has a backwater check valve, you usually can access it near the main sewage cleanout. If you have an older home or are unsure if you have such a valve, have a licensed contractor install one.

Some homes may have slice valves. You generally can access slice valves through a holdout in the basement floor and turn them off and on easily in the event of flooding or sewage backup.

If you do not have a backwater or slice valve, you can install plugs in drains. Here are some plugs that might work for you:

• Test ball: It’s used for pressure-testing plumbing systems but can be used in emergency situations to seal drains. You insert the ball into the drain pipe and inflate it with air to the prescribed air pressure. Once inflated, the ball will not allow water to flow in either direction.
• Twist plug: You insert it into the pipe and twist the wing nut until the plug is tight. Twist plugs come in a variety of sizes and work well with floor, shower and toilet drains.
• Pressure plugs: These are conical-shaped rubber or wooden plugs. They’re smaller in diameter than the pipe to be plugged on one end and larger than the pipe on the other end. You force them into the pipe. You also may need to brace them to prevent pressure from pushing them out.
• Threaded screw caps: You need to remove the plumbing fixture and insert the correct-sized cap in the pipe.

Plugs or threaded caps work best if you can remove the drain grates or other fixtures. If you can’t remove the grates, other methods can be effective. One method is to place a piece of inner tube that is larger than the drain hole on the area surrounding the drain and cover it with a piece of plywood or solid board to hold it in place. Particle board will not work because it can deteriorate and crumble when wet.

The tubing and board should be held in place by bracing it against the ceiling. To avoid damaging the ceiling, place a 2- by 4-inch board or piece of plywood parallel to the ceiling. Then wedge a vertical 2- by 4-inch board between the board covering the inner tube and the board parallel to the ceiling.

Here is how to plug specific types of drains:

• Toilet: Turn off the toilet’s water supply, remove the water line from the toilet, press the plunger to flush the toilet and empty the water tank, remove as much water as possible from the bowl by pouring a bucket of water into the bowl as fast as possible without spilling, remove the two bolts holding the toilet and remove the toilet, then insert a plug in the drain.
• Washing machines: Remove the drain hose from the washing machine and place the correct diameter plug in the drain pipe. Installing threaded-cap plugs in the drain is preferable.
• Sinks: Place a plug in the sink drain and overflow. The preferred method is removing the drain pipe from below the sink and placing a threaded cap on the drain outlet.
• Bathtubs: If you have an access panel for the bathtub plumbing, remove the drain pipes and install drain plugs. If you don’t have access to the internal plumbing, use a twist plug in the drain. To plug the overflow, remove the overflow cover and install a properly sized drain plug. You may need to purchase an automotive or marine plug because the overflow drain is shallow.
• Showers: If you can remove the drain grate, simply place the proper sized drain plug into the drain pipe and tighten it until it is snug. If you can’t remove the grate, cover the drain with a thick piece of rubber or inner tube and use the bracing method described for floor drains.

Pedersen also recommends you remove floor grates or plumbing fixtures and measure the diameter of the pipe so you will know what size plug you will need before heading to the hardware store.

“Each home and drain can be different, so do not assume your home has a standard size for each application,” he says. “The key is to plan and prepare well in advance.”

For more information on plugging drains, check out NDSU’s new publication, “Plugging Home Drains to Prevent Sewage Backup,” at http://www.ag.ndsu.edu/pubs/ageng/structu/ae1476.pdf. For other help in preparing for flooding, visit http://www.ag.ndsu.edu/flood.

NDSU Agriculture Communication