How the valve works
A normally open backwater valve sits in the main building drain under the basement floor. Wastewater from the house pushes through freely. When sewage tries to flow backward, a flap floats up and seals the pipe. Once the surge passes, the flap drops and normal flow resumes.
What it protects and what it does not
- It stops sewage from the city main entering through floor drains, toilets and tubs
- Groundwater seeping in through walls or the slab is not something it can stop
- It does not help if your own lateral is blocked by roots
Living with a valve
- Lift the access cover once a year and look at the flap.
- Clear any debris or paper caught on the seat.
- Check that the floats or flap move freely.
- During a severe storm, use as little water as possible, since your own drains are closed off while the flap is shut.
Inside the access box
Lift the cover and you will see a clear or black plastic lid bolted over the valve body. Unscrew it and you can see the flap or gate, which should swing freely. Debris like paper or grit can stop it sealing, so rinse it with a hose. Put the lid back carefully, with its gasket seated, so sewer gas cannot escape.
Permits and programs
Installation normally needs a plumbing permit. Richmond Hill has run flood-protection subsidy programs before; read the City's current terms before booking. Our installation page explains the work, and basement flood prevention covers the rest of the plan.
Keep-handy checklist
- Shine a light under each vanity and kitchen sink every spring and fall
- Pencil the install date on the water heater and the sump pump
- Pull the pop-up stopper and clear the hair every couple of months
- Pour a pail into the sump pit before the thaw and watch it cycle
Your questions, answered plainly
Does every house need one?
Homes with basement fixtures or floor drains below street level benefit most.