The Use of Check Valves in Basement Drains

Check valves allow the flow of liquids or gasses in only one direction. In a basement plumbing application, this means the valve allows water to flow out of the basement but prevents backup of liquid into the basement. Properly installed this reduces or eliminates the possibility of wastewater backup through a basement floor drain or sump pump.

How It Works

The check valve includes a small floating ball or cone in the valve opening.  Flows of water from the top of the valve push the float down and away from the seal and allow the water to flow down the drain.

Flows of water from below the valve push the float up against the seal and prevent the flow of water up through the valve and into the basement. 

Installing the Check Valve

Install the check valve with the top at floor level of the basement.  The check valve does restrict the amount of water flowing through the valve so a check valve larger than the original drain size may be appropriate.

The valve installs above a trap in the drain line.  The best time to install a check valve is during the initial construction of the home when basement plumbing is installed.


Add a little water down the drain every week to keep the trap full.  A check valve only stops liquids, not sewer gas, from backing up into the home.

Make sure the float ball or cone moves freely within the valve.  Remove any debris that would interfere with the movement of the float.

Basement Uses

Homeowners use check valves in basement floor drains or sump pumps only.  The valve does not prevent sewage backups that reach the level of basement toilet bowls or other lower level fixtures.

Use other forms of drain plugs in basement fixtures if sewage backup is a concern. 

About the Author

Keith Allen, a 1979 graduate of Valley City State College, has worked at a variety of jobs including computer operator, medical clinic manager, radio talk show host and potato sorter. For over five years he has worked as a newspaper reporter and historic researcher. His works have appeared in regional newspapers in North Dakota and in "North Dakota Horizons" and "Cowboys and Indians" magazines.