Sewer Backup Prevention Valve FAQs

Q&A on use of Backwater Valves & Toilet Plugs to Prevent Sewer Backups

What's the difference between a simple floor drain check valve and a backwater valve?

Please explain the difference between purchasing a $15 floor drain check or having a backwater value installed. Thanks. On 2017-07-06 by Mary

by (mod) - check valves that can be installed right at a floor drain protect just that drain, and are simpler than a backwater valve.

Mary,

There are check valves that can be installed right at a floor drain that may prevent sewage from backing up through the drain onto the floor. That device only prevents backups at the drain itself.

Photo above: a Moen M8082 M-Line Series Floor Drain Check Valve made of brass that costs about $15. U.S.

Illustrated below: a Full Port 4953 Main Sewer Line Check Valve [PDF] from AB&A, an IPS Corporation

Note: in our annotated photo of the Main Line Backwater valve above we've put a red arrow showing the flow direction arrow. The backwater valve is always installed with the arrow pointing towards the exterior of the building or the sewer line exit direction towards the street (or towards the septic tank).

So if site elevations and sewer or septic piping were such that a sewage backup could move to a higher level you might find a sewage backup up into a basement washing machine or shower or sink even though the lower floor drain remained sealed.

A backwater valve such as the Fullport 4-inch Main Line backwater valve model shown above (product details) [PDF] (local copy saved as Mainline-Full-Port-Flye.pdf) ($170.) or as another example the Canplas 223254WPK1 PVC Fullport Backwater Valve, 4-Inch unit ($225.) is designed to be installed at the building sewer line at its point of exit from the structure.

That valve will prevent sewage from entering the whole building's drain system from that point into the building, thus protecting higher fixtures or drains as I suggested above.

Of course the costs for the two parts are different.

A main drain backwater valve like the one we show just above and in more detail below may retail between $40. and $250. USD. before installation while a floor drain check valve might retail from $15. to $60. USD before the installation costs.

Installation cost for a backwater valve or for a floor drain check valve will vary widely for either valve depending on

- where you live and local plumbing rates

- the difficulty or ease of access to the installation location

- the necessity to cut out concrete to install the drain device

Figure $50-$250 for a floor drain valve installation, again depending on type of floor drain check valve device selected and the need to chop concrete

Figure a minimum of $150. and more-likely $250-$500. for a main sewer line backwater valve.

Can I install a second backflow check valve to protect against failure of the first one?

I have a Backflow Prevention (Check) Valve installed on my main drain line just outside my house. Can I install a second Backflow Check Valve just before the sidewalk as "double protection" (in case one fails)? (June 2, 2015) anonymous

Reply: double backflow prevention valves are permitted and even required in some cases

Yes. In some situations and jurisdictions double backflow prevention check valves may even be required. Check with the manufacturer for the speciific product you intend to use.

How to stop toilet paper from getting stuck in the check valve

Does anyone have any advice on how to stop toilet paper from getting stuck in the check valve and subsequently leaving the flap open and vulnerable to backwater flooding?

Is there anything I could do to get it unstuck from the toilet side without opening the valve itself? On 2018-11-09 by LANA

by (mod) -

If you're using I whole house sewer line full port check valve it's supposed to be self cleaning. It shouldn't be jamming with toilet paper. So perhaps we have the wrong valve installed or its installed in the wrong position.

I assume you're dreaming by gravity. If you have a check valve in a force main that's clogging then I suspect it's the wrong pump and a macerating sewage pump is needed.

Trouble finding a backwater valve or check valve that works on a vertical drain line section

I've found very few vertical backwater (backflow prevention) valves, which seem like they'd be much cheaper to install in situations where the main pipe to the public sewer comes underground, then up vertically in the basement, since there would be no digging through cement.

Is there a reason not to use a vertical valve? On 2018-02-17 by Mark G

by (mod) - Not all of these check valves can work vertically.

Mark

Watch out: Not all of these check valves can work vertically. I speculate that's because it's a more costly as and challenging design requiring a stronger closing spring that has to be overcome by water flowing by gravity down the drain.