How to Check Sewer Flap Valves

Flap valves are one of two different types of valves installed in homes and buildings to prevent water and sewage back flow from re-entering the home or building. Along with gate valves, they are generally located in one's basement, or outside the home near where the sewer and waste pipes exits the home. Flap valves work by automatically closing when water or sewage flows in reverse, back into the home. They require no manual operation, but should be checked for proper operation periodically.

Pipe wrench
Plumber's grease or irrigation tape
Gloves
Gasket replacement kit if necessary

Instructions

- 1
  
  Sewer pipe may be plastic, cast iron or even clay.
  
  Locate your waste line's flap valve. It will have a PVC domed cover cap or, in older homes, may be metal.
- 2
  
  Make sure to use a pipe wrench that will open wide enough to remove cap.
  
  Use the plumber's wrench to unscrew the cap. If it has been a lengthy period of time since it was last checked, it may require some lubrication to open.
- 3
  
  A gasket is a plastic or silicone material that makes a seal.
  
  Check the valve's operation manually by opening and closing. Always wear gloves when doing this. Check the gasket on the valve, if there is one, for cracks or misalignments.
- 4
  
  A flat head screwdriver may need to be used to scrape off the old gasket.
  
  Replace the gasket if worn. Remove the old gasket entirely before installing new one. Then the water to the house off while doing this.
- 5
  
  It may be necessary to have someone assist by flushing the toilet inside while you're checking the flap valve.
  
  Test the gate valve's operation by running water or flushing a toilet. If all is working properly, no further check is required.
- 6
  
  Irrigation tape is usually made of Teflon.
  
  Apply plumber's grease or irrigation tape to the threads on the cover prior to reinstalling. This will make it easier to re-open the next time you check it.

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