How a backwater valve works
It lives in the big drain under your basement slab, after the last fixture and before the city pipe. Day to day its gate hangs open and waste passes freely. Reverse the flow and floats lift the gate against its seat. During that time your own wastewater is trapped too, so you avoid running water during the storm.
The installation
- We camera the main line to find its depth and condition and choose the valve location.
- The basement floor is saw-cut and broken out over the line, usually near the front wall.
- We remove a length of pipe and drop the body in dead level, arrow pointing toward the street.
- A riser and lid go on top so you can reach the gate for cleaning.
- The trench is backfilled and the concrete restored.
Markham generally expects a permit for this job. Ask us, and check the City of Markham building department for current requirements.
The visit, in order
- 1
Pull the old pump, clean grit out of the pit and inspect the liner.
- 2
Seat the replacement pump on a level paver so its float travels freely past the liner.
- 3
Fit the check valve and union, then run the discharge outside and away from the foundation.
- 4
Pour water into the pit until the float lifts, then watch one complete start-and-stop cycle.
Subsidies
Markham has run a basement flooding protection program that has helped eligible homeowners with the cost of backwater valves and related work. Terms, amounts and paperwork change, so confirm current details directly with the city before booking, and keep receipts and permits.
| Valve type | Typical use |
|---|---|
| Normally open mainline valve | Most homes; allows venting and full flow |
| Inline valve on a branch | Protecting one fixture group where a mainline valve is impractical |
Looking after it
Each spring and fall, pop the lid, swing the gate with a gloved finger and fish out anything lodged inside. Our guide to backwater valve maintenance walks through it. Combine with sump pump installation where groundwater is also a concern.
Markham note: village-core houses tend to hide cast iron and galvanized behind plaster, while Cornell and Box Grove builds run PEX to a manifold. We ask the year your house was built so the right fittings ride along on the truck.
Straight from the phone log
Does a backwater valve stop all basement flooding?
No. It stops sewer backup through drains. Water creeping through the walls or slab calls for weeping tile and a sump.
May I shower while the gate is shut?
Avoid it. Water from your fixtures cannot leave and could back up into the basement.
Ready to get it fixed?
One call, a clear explanation, and work finished tidily before we leave.