Backwater Valve Maintenance

How the valve does its job

The valve is set into the house drain, below the basement slab, usually close to the front wall. A hinged flap lets sewage flow out of the house but swings shut if sewage tries to flow back in from the city sewer. A clear cover on top lets you look inside.

How often to check

Look at it at least once every spring, and after any heavy storm or drain problem. Many owners do it in spring, alongside a sump pump test.

The inspection

1. Make sure nobody uses water in the home during the check.
2. Remove the access cover over the valve, following the maker's instructions.
3. Inspect the flap. It ought to swing without catching and lie flat on its seat.
4. Clear any paper, grease or debris from the flap and seat with gloved hands.
5. Check the cover gasket is intact before closing.

Problems we find

• A flap held open by a wad of wipes or grease.
• A cover that was never resealed properly, letting sewer gas into the basement.
• A valve installed on the wrong line, so it does not protect the floor drain.
• A valve buried under flooring with no access.

Using drains during a backup

While the valve is closed during a city sewer surge, water from your own fixtures cannot leave the house. Running the washer or flushing toilets then can flood the basement from the inside. During heavy storms, limit water use.

See backwater valve installation and our flood checklist.