17 Years Toronto Plumbing CSA B64.10 Certified WSIB & $2M CGL Repeat-Flood Homes

Dual Flapper Backwater Valve Installation in Toronto, ON | Licensed, Permitted & Rebate-Ready

Last updated: October 6, 2026 · By The Backwater Valve Toronto Crew

Backwater Valve Installation Toronto installs dual flapper backwater valves for Toronto homes that can't afford a second flood. A normally-open primary flapper keeps your drains and vent stack clear, and a secondary flap closes if wipes or debris hold the first one open during a surge. A licensed plumber pulls the City of Toronto drain permit, sets the valve in an interior pit or exterior trench, backflow-tests both flaps and files the Toronto Basement Flooding Protection Subsidy. You recover up to $1,250, or $1,750 with a sump pump. After 17 years, this is the valve we pick for our own repeat-flood customers.

Dual flapper installs run $2,200-$3,800 per install before the rebate. We spec Mainline Backwater Valves, Mustee or Zurn models, with normally-open flapper or dual-flapper configurations depending on sewer lateral depth and risk tolerance. Every install includes drain permit coordination, backflow test certification, City inspection booking, and rebate paperwork across North York, Scarborough, Etobicoke, Toronto East, Toronto West and the rest of the GTA. Written 2-year workmanship warranty, WSIB coverage, $2M CGL.

Same $1,250 Subsidy as a Single Valve

The second flap doesn't reduce your rebate. Add a sump pump for $1,750 total.

From $2,200 per install, before rebate See full pricing

Book Free In-Home Drain Assessment

Includes sewer lateral camera scope and subsidy verification

Property Address / Neighbourhood

Phone Number

Installation Type Needed

I confirm I am the property homeowner or authorized property manager eligible for City of Toronto subsidy filing.

Written 2-Year Workmanship Warranty + City Permit Coordination

17 Years of Toronto Backwater Valve Experience
Backflow Certified to CSA B64.10
WSIB Registered, $2M CGL
2,400+ Installs Completed

Engineering Specifications

How a Dual Flapper Backwater Valve Is Built

Two flaps, one valve body, and a clear cover so you can see both working.

Primary Normally-Open Flapper

The primary normally-open flapper is the same design we use on a standard Mainline MBV install. A float-activated gate rests open, so wastewater flows out freely and sewer gases can vent up through your stack the way the plumbing was designed. When sewage starts moving backward from the street, the float lifts the flapper shut against its neoprene gasket. That happens in seconds, before water can reach the floor drain. Because it sits open, the primary doesn't restrict flow or cause gurgling. It's sized to your 4-inch or 6-inch lateral, tested to CSA B64.10, and approved for the City of Toronto subsidy. On its own, it's very good. The second flap covers the times it isn't.

Secondary Backup Flapper

The secondary backup flapper exists for one reason: things get stuck. Flushable wipes, grease clumps, root fragments and the odd toy can lodge in a primary flapper and hold it slightly open just when a sewer surcharge arrives. A dual valve puts a second, independent flap downstream inside the same body. If the primary can't seal, the secondary closes on its own gasket and holds back the surge. Each flap has its own hinge pin and seal, so one failing doesn't affect the other. We check both seat cleanly during the install and during every annual inspection. In our experience, this redundancy is what keeps repeat-flood basements dry through the worst Toronto storms.

Air Vent and Clear Access

The air vent and clear access cover make a dual valve easier to live with. An air vent accessory lets the valve body breathe when both flaps are moving, which stops the gurgling and slow drains some homeowners notice with older valves. The clear polycarbonate cover sits on top of the valve body, flush with your floor or under a removable plate, so you can see both flaps without unbolting anything. Once a season, lift the plate and look: both flaps should rest in their normal positions with no debris on the seats. If you spot buildup, the cover comes off with a few bolts for cleaning. We show you exactly how before we leave.

When Dual Beats Single

A dual valve beats a single in three kinds of homes. First, repeat-flood houses, where the basement has backed up more than once and the street clearly surcharges. Second, finished basements with flooring, drywall and furniture worth far more than the $400-$600 upgrade. Third, low-lying lots, such as lakefront homes in Mimico, Long Branch and The Beaches, where surge pressure is higher and more frequent. The trade-off is maintenance: two flaps take a few minutes longer to check, and dual bodies cost more. For a dry, unfinished basement on high ground, a single normally-open valve is usually enough. We'll tell you honestly which one your home needs at the free assessment.

3 Homes That Should Choose a Dual Flapper Valve

The home that’s already flooded twice. If your basement has backed up more than once, your street surcharges and will again. A second flap is cheap insurance against a stuck primary.
The fully finished basement. When the space below grade holds a bedroom, a home office or a theatre, the cost of one failure dwarfs the $400-$600 upgrade. Pair it with a careful interior backwater valve installation that protects your finishes.
The low-lying lot. Lakefront homes in Etobicoke and The Beaches, and homes at the bottom of a hill, see stronger, more frequent sewer surges. Redundancy matters most where pressure is highest.

A Watts BV-100 or Mainline dual body fits most interior pits we cut for a single valve, so the upgrade doesn’t usually mean a bigger hole.

Do I Really Need Two Flappers?

In our opinion, not every home does. A well-installed normally-open single valve, tested and checked once a year, protects most Toronto basements. The second flap earns its keep when debris is likely and the cost of failure is high.

The honest trade-off is maintenance. You have two hinges and two gaskets to inspect, which adds a few minutes to the annual backflow test. If you already have a single valve that’s aging or failing, a backwater valve replacement can swap it for a dual body in the same pit. We’ll price both options side by side at your assessment.

Why Toronto Homeowners Trust Us

Why Choose Backwater Valve Toronto for Dual Flapper?

Seventeen years and 2,400+ installs across North York, Scarborough, Etobicoke and central Toronto.

1 City Rebate Expertise

Dual valves earn the same $1,250 subsidy, and we file it for you on every install.

2 Licensed Toronto Plumber

Installed by a licensed Toronto plumber, with ECRA/ESA trades on any sump pump circuit.

3 Both Flaps Backflow Tested

We test the primary and the secondary separately to CSA B64.10 before the pit is closed.

4 Honest Single vs Dual Advice

If a single valve is enough for your home, we'll say so and save you the upgrade.

5 Published CAD Pricing

$2,200-$3,800 posted openly, with what moves the price explained below.

6 Written 2-Year Workmanship Warranty

Covers the install of both flaps, the air vent and the access cover.

Zero Hassle Process

How Our Dual Flapper Process Works

How The Backwater Valve Toronto Crew protects your basement and files your City rebate.

Step 1
In-Home Drain Assessment and Camera Scope

We inspect the main drain, find where the sewer lateral leaves the house, check slope, and confirm whether the pipe is clay, cast iron or PVC. We also confirm your subsidy eligibility. The visit and camera scope are free.
Step 2
City of Toronto Drain Permit

We apply to Toronto Building for the drain permit on your behalf before any concrete is cut. No permit means no subsidy, so we never skip this step.
Step 3
Interior Pit Excavation or Exterior Dig

Dust-shrouded saw cut inside, or a shored excavation at the property line outside. The valve is set on 3/4-inch clear stone bedding with cleanout access.

Some installers skip the backflow test, which voids both the warranty and the subsidy. We test every valve under load.
Step 4
Valve Installation, Backflow Test and Mitchell Harrington Quality Review

We backflow-test the new valve, record the results and photos, and founder Mitchell Harrington reviews the test documentation and CSA B64.10 compliance before the pit is closed.
Step 5
City Inspection and Rebate Submission

The City inspector signs off, then we file the Basement Flooding Protection Subsidy paperwork. The cheque typically arrives 6-8 weeks after submission.

Want a written price for dual flapper before you commit?

The assessment and camera scope are free. You see the CAD price in writing before any work starts.

Call (416) 555-0199 Book Free Assessment

Transparent CAD Pricing

Dual Flapper Backwater Valve Cost in Toronto

A dual flapper backwater valve in Toronto costs $2,200-$3,800 CAD installed, before the rebate. That's roughly $400-$600 more than a single-flapper interior install, for the larger valve body, the air vent accessory and the extra test time.

The City of Toronto subsidy is the same up to $1,250, so a $3,000 dual install costs about $1,750 after the cheque. If your home also needs a sump pump, combining them qualifies for $1,750 back in total.

What affects the price	How it moves your quote
Interior pit or exterior trench	Exterior placement adds excavation and restoration.
Lateral size	6-inch dual bodies cost more than 4-inch.
Floor finish over the pit	Tile and plank need careful removal and cover templating.

Published Price

Dual Flapper $2,200 - $3,800

per install, before rebate

Eligible for up to $1,250 City subsidy

Normally-open primary flapper for unrestricted drainage and venting
Secondary backup flapper for redundancy
Air vent accessory and clear access cover
Backflow test on both flaps

Get My Exact Price See every price band

On The Job

Recent Dual Flapper Work Across Toronto

Group crew photos from real Toronto basements and property lines. Tap any photo to enlarge.

Customer Proof

What Customers Say About Our Dual Flapper

"After a flood in 2024 I wanted the backup flap. They explained the cleaning trade off and I still went dual. Two big storms this summer and the basement stayed dry."

Kevin L., Riverdale

Dual flapper install $3,300 CAD

"The clear access cover sold me. I can see both flaps without unbolting anything, and the air vent stopped the gurgling we used to get."

Sandra P., Mimico

Dual flapper install $2,900 CAD

Clear Answers

Dual Flapper FAQs

How much is a dual flapper backwater valve in Toronto?

$2,200-$3,800 CAD before the rebate. The subsidy amount is the same as for a single-flapper valve, up to $1,250.

Does a dual flapper valve need more maintenance?

A little. There are two flaps to check, so the annual inspection takes slightly longer, but the clear cover makes visual checks easy.

Which dual flapper models do you use?

Normally-open primary flapper designs from Mainline MBV and Watts, with a secondary flap and air vent accessory.

Is a dual flapper worth it in The Beaches?

Often yes. Beaches homes sit low near the lake with century clay drain tiles, so redundancy pays off when debris holds the primary flap open.

Can I upgrade my single valve to a dual?

Usually, by replacing the valve body in the existing pit. We check that the pit has room for the longer body and confirm subsidy eligibility before you book.

Will a dual valve slow my drains?

No. The primary flap rests open and the air vent accessory lets the body breathe, so drainage and venting work normally.

What happens if both flaps get stuck?

It's very unlikely, because each flap has its own hinge and seal. The annual check catches buildup long before both could fail.

Is the dual valve approved for the City subsidy?

Yes. The models we install are City-approved, and the second flap doesn't change your eligibility.

Still have a question?

A licensed plumber can answer it on the phone or at your free assessment.

Call (416) 555-0199

Keep Exploring

Installation Types

Interior Backwater Valve Installation

Pit-based backwater valve installed under your basement floor, with drain permit, backflow test and subsidy filing included.

$1,800 - $3,200 Details →

Service and Maintenance

Backwater Valve Replacement

Swap an aged or failed valve for a current City-approved model, usually reusing the existing pit.

$1,500 - $3,000 Details →