How the valve works
Expect to find it in the floor slab of the basement, typically toward the street side where the sewer leaves. Inside is a hinged flap, often with a float. Normally the flap rests open or lightly closed and household waste flows out. When the sewer main backs up, rising water pushes the flap shut and blocks the reverse flow. Once the surge passes, it reopens.
With the flap shut, your own wastewater is trapped indoors too. So while the street sewer is overloaded, avoid running the washer, dishwasher or showers.
Finding the lid
Search for a round or square cover in the basement floor, often with a clear or screw-down lid. On some installations it is boxed under a removable panel in a finished floor. The cover must stay accessible. Flooring, carpets and storage on top of it defeat the purpose.
Give the drains an hour of rest first, with no taps, flushes or appliances running, so the line is quiet. Wear gloves and eye protection. Keep a bucket, rags and a flashlight ready.
Cleaning
- Unscrew or lift the access cover.
- Work the flap by hand: it ought to swing without binding and close tight on its seat.
- Remove any debris, grease, wipes or hair caught on the flap or in the channel.
- Rinse the flap with a garden hose or a bucket of clean water.
- Check the floats and the gasket on the cover for damage.
- Replace the cover snugly so it seals.
Follow the manufacturer's instructions for your model. Some valves lift out for cleaning; others are serviced in place.
Warning signs
- Slow drains across the basement, suggesting a flap stuck partly closed.
- Sewer odour near the cover, which may mean a loose lid or failed gasket.
- Water on the floor around the cover during heavy use.
- A flap that will not close because of debris or a broken hinge.
Wipes, grease and paper towels are the usual troublemakers. Our note on what not to flush explains why they cause trouble far beyond the toilet.
When to call
If the flap is cracked, the hinge broken or the seat damaged, a repair or replacement is needed. Some flooding events also leave sediment that needs flushing beyond what a homeowner can do. If you are considering a valve for the first time, our backwater valve installation page explains the work; Durham towns have run rebate programs for these valves at times; confirm current terms with Whitby before you book. For persistent drain issues near the valve, start with pipe repair or a camera.
Write the date of each inspection on a piece of tape inside the access lid. It takes seconds and removes any doubt about when the valve was last opened.
Asked on the phone
How often should I clean a backwater valve?
At least once a year, and ideally before spring and autumn wet seasons.
Can I use water while the valve is closed?
No. When it closes during a surge, your own wastewater cannot leave either. Hold off on laundry and showers.