Top Check Backwater Valve
and Top Check Backwater Valve Parts

Mainline Top-check Backwater Valves in 4" PVC

These 4" PVC Top check Backwater Valves drop 1" from Inlet to Outlet

  • This revolutionary new Mainline TopCheck Backwater Valve design features an automatic top suspended gate that can also be closed manually.

top check backwater valves

  • The gate requires requires minimal maintenance and stays clean and ready to protect your dwelling from sewer backup events!

  • The clear plastic lid also integrates a manual sewer shutoff allowing for easy manual closure if you know a backup event is likely, or you leave the dwelling

  • We offer this package with Access Box, Bladder Seal and Alarm System!

This Top-Check Fullport Backwater Valve is Mainline’s newest an most advanced automatic backwater valve.  The top-suspended gate is up and out of the normal flow of waste so stays clean and ready to protect. This is a normally-open gate automatic backwater valve design.

A unique design feature in the clear polycarbonate inspection lid allows the owner to easily twist a red shut off to manually close the valve gate

The clear plastic lid allows for easy visual inspection and a removable black plastic lid for cleaning or main sewer line snaking / rodding.

The Schedule 40 PVC (poly vinyl chloride) 4" DWV valve body is sturdy and durable.

Black ABS Access Box with removable access panel Included!

Mainline Top-Check fit backwater valve pricing

Straight Fit Normally Closed Gate 6SF-GateNC

Mainline Bladder Seal

Bladder Seal Included!

Seals the dwelling against groundwater flooding through the box.

Seals against insects / bugs from entering dwelling through the box.

Ensures nice clean access to your TopCheck Backwater Valve free of concrete, gravel, sand, mud and water once installed over the access box.

Protects against radon gas from entering your dwelling and easily integrates with any existing vapor barrier system.

Mainline Top-Check fit backwater valve pricing


Top Check Backwater Valve Alarm System Included!

This is an integrated backwater valve flood alarm for the Mainline Top-Check Backwater Valve, powered by a standard 9V battery.

It can be easily installed by simply inserting an included magnet into a factory-provided slot in the Top Check Backwater gate, installing an electromagnetic sensor on the outside rim of the clear plastic cover adjacent to the magnet, and connecting the included wiring he Alarm Box.

The box emits a loud, shrill tone (similar to that of a smoke alarm) to alert you  when your Backwater Valve is in active and protecting you from a sewer line backup.

Mainline Top-Check fit backwater valve pricing

Top Check Backwater Valve brochure in Adobe Acrobat pdf file format
VIEW Top-Check Alarm brochure here

top-check valve alarm


Patented in USA # 5406972
Patented in Canada # 2114602
Other patents pending
Made in Canada
ASME A112.14.1-2003(R17)
CSA B181.1-02 and CSA B181.2-2018
UPC Compliant
National Plumbing Code of Canada Compliant
International Plumbing Code (IPC) Compliant

This product has been tested by an IAPMO R&T recognized laboratory. This recognition has been granted based upon the laboratory's compliance to the applicable requirements of ISO/IEC 17025.


Top Check Backwater Valve brochure in Adobe Acrobat pdf file format
VIEW the IAMPO Certification Sheet here

 top check backwater valve measurements

Top Check Backwater Valve brochure in Adobe Acrobat pdf file format
View the ToCheck Backwater Valve brochure here

Mainline Top-Check fit backwater valve pricing


top check backwater valves backwater check valves backwater valves adapt-a-valve information ml fr4 fio valve information termex valve information straight fit backwater valves backwater valve diagram backwater valve features and specifications backwater valve history testimonials backflow prevention information helpful links backwater valve pricing frequently asked questions backwater valve specifications backwater valve installation tips backwater valve animation backwater valve videos contact us backwater valves main page backwater valves backflow prevention links


backflow check valve products



adobe acrobat pdf filesAdapt-A-Valve Brochure (Adobe Acrobat pdf)

Adapt-A-Valve Inspection Chamber

Backwater Valve Diagram
Backwater Valve Features
Back water valves information
Backflow Links
Backflow Preventers
Backwater Valve Animation
Backwater Valve Videos

Basement Drain Backing Up

 contact us about your backwater valve needsContact Us

Flood Alarm

Frequently Asked QuestionsBack water valve questions

adobe acrobat pdf filesFullport Backwater Valve Brochure (Adobe Acrobat pdf)

how to install your backwater valveINSTALLATION TIPS;  how to install backwater valves 

Termex Backwater Valves
Termex Backwater Valve Brochure (Adobe Acrobat pdf)

NEW: TOP-CHECK BACKWATER VALVESnew Top-check backwater valves

Mainline ML-FR4 Backwater Valve (Fio Valve)
adobe acrobat pdf filesML-FR4 Mainline Backwater Valve Fio Valve Brochure (Acrobat pdf)

6" Backwater Valves - Mainline STRAIGHT FIT Backwater Valves

Mainline History

backwater valve measurements and specificationsMeasurements, Specifications and IAPMO Certifications


Mainline Fullport Backwater Valves offer the right solution for your sewer backup problems.


Protect Your Home with a Backwater Valve

All Orders must be placed ONLINE by Credit Card


telephone For non-order info, you may phone Greg at 330.836.9393 9 AM - 4 PM EST M-F
or Voicemail anytime)


copyright 2004 to 7/15/2024 at 9:44:32 ET,
Akron, OH, USA.
All rights reserved.

backflow prevention links is independently owned and resells products produced and manufactured by Mainline of Canada and assumes no liability for the installation of backwater valves and related products.

Be sure to check with the plumbing authority in the municipality in which your valve is to be installed to insure that your installation is in compliance with local code, and be sure have your valve inspected by your local plumbing inspector after installation. Inspect your valve frequently; the Backwater Valve through its clear plastic housing top, and the Adapt-A-Valve, by removing the gate cassette.


Pipe end-to-end, the Adapt-A-Valve takes up 6" of run in your line and the outlet is 1-1/2" LOWER than the inlet, so in just 6" the level of the pipe at the outlet side needs to be 1-1/2" lower.

Pipe end-to-end, the Backwater Valve takes up 12" of run in your line and the outlet is 3/4" LOWER than the inlet, so in just 12" the level of the pipe at the outlet side needs to be 3/4" lower.

Depending upon the amount of slope in your line (2% minimum is required for proper operation), you may need to replace several feet of pipe downstream from the valve to average out this "loss" of fall.

NOTE: New Straight-Fit and ML-FR4 require less slope. (refer to detail pages for these products)


Mainline Valve Warranty
(in printable Adobe Acrobat .pdf file)

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