6" Backwater Valves

Mainline Straight Fit Extendable Backwater Valves in ABS and PVC

These 4" and 6" Backwater Valves drop less than 1/2" from Inlet to Outlet

The newly crafted Mainline ML-SF668 Extendible Backwater Valve is a great choice for new and retrofit situations where a 6" valve is needed.

3" ML-SF334 & 4" ML-SF446 Extendable Backwater Valves are also available now.

The STRAIGHT-FITTM valve is Mainline’s latest addition to the Extendible Backwater Valve series.  This is a normally-closed gate automatic backwater valve design.

STRAIGHT-FITTM valves come in 4” and 6” (both models are now available) and have features that will make STRAIGHT-FIT one of the most asked for valves in the industry!

Produced in both Schedule 40 PVC and ABS, the STRAIGHT-FITTM has a body that is extendible to whatever depth you require by simply gluing a riser of Schedule 40 (like material) pipe into the valve body and extending to ground level.  The 6" valve uses an 8" diameter riser and the 4" valve uses a 6" diameter riser.  This sourced on the jobsite and cut-to-size on site riser is to be capped with an air-tight cap.

The normally closed gate is glued to a piece of ¾” PVC pipe (sourced on the jobsite and cut on site to proper length) to form a tool to extract the gate from the valve body.

Mainline has integrated "Smart-CURVE"TM technology into these valves which serves as a dual function;  First, this system features a "curved gate" that is designed to allow a sewer rodding snake to feed and retract without catching on the gate itself!  The other added benefit is a "Smart-CURVE"TM "cleat insert" in the body that will ease and guide the retrieval of the snake without hanging up on the body

 The STRAIGHT-FITTM also features an optional Test Gate that can be used to pressure test the system or to isolate the property for whatever purpose; non -payment of services, vacation properties, servicing etc.

Patented USA 4503881 and Canada 1196835; other patents pending.  ASME A112.14.1-03, CSA B181.1-02 and B181.2-02, UPC US 8.096.318 and Canada 7.757.706 and 2.414.634.

VIEW IAMPO Certification Test Results here

Mainline ML-SF668 PVC Straight Fit Backwater Valve

Mainline ML-SF668 ABS Straight Fit Backwater Valve

top view -ML-SF668 ABS straight fit extendable backwater vavles Straight Fit Normally Closed Gate 6SF-GateNC
top view - ML-SF668 PVC straight fit extendable backwater vavles ML-SF668 Valve with PE-2013 Access Box Combo

Optional 3", 4" and 6" Test Gates offer test mode or 100% Manual Seal

3" Straight-Fit Backwater Valve Test Gate 4" Straight-Fit Backwater Valve Test Gate 6" Backwater Valve Test Gate

Straight Fit Backwater Valve SF668 brochure in Adobe Acrobat pdf file format - Mainline ML-SF668 ABS/PVC Valve Brochure (Adobe Acrobat pdf) - Mainline ML-SF668 straight fit backwater valve pricing


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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
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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

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backwater valve measurements and specificationsMeasurements, Specifications and IAPMO Certifications


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


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backwater-valves.com 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)


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(in printable Adobe Acrobat .pdf file)

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