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Sewer line backup prevention: This document explains for homes connected to a municipal sewer we discuss how to prevent sewer or storm drain backups into a building during rain or heavy flooding including the installation and use of backflow preventers, backwater valves, check valves and toilet drain plugs.

The sewer line back flow prevention valve shown at page top is produced by Mainline Backflow Products - Backwater Valves (image use permission requested).

If toilets are overflowing, see TOILET OVERFLOW EMERGENCY. If your building drains are already backing up, especially during a time of heavy use such as with guests in the home, see SEPTIC BACKUP REPAIR or for homes connected to municipal sewer, see CLOGGED DRAIN DIAGNOSIS & REPAIR.

If your sewer or septic system uses a sewage pump, be sure to review SEPTIC PUMPS and SEWAGE PUMP CLOG DAMAGE.

Citation of this article by reference to this website and brief quotation for the sole purpose of review are permitted. Use of this information at other websites, in books or pamphlets for sale is reserved to the author. Technical reviewers are invited and are listed at References.

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Guide to Preventing Septic or Sewer Backups Due to Flooding or Sewer Main Backups

If toilets are overflowing or not flushing, see TOILET OVERFLOW EMERGENCY. And for emergency toilets, see Camping & Emergency Toilets.

If your home is connected to a private septic system and drains are already backing up, especially during a time of heavy use such as with guests in the home, see SEPTIC BACKUP REPAIR.

Late Night Sewer Backup Starts Washing Machine in the Basement

One of our clients in Cold Spring New York reported waking during the night to hear their old basement clothes washer running. Having just moved into the home the occupants wondered what ghost was doing laundry at 2 AM. Investigating they found that the local municipal sewer had backed up into the home through the main drain line.

Because their washing machine drain was improperly connected (without an air gap) to a drain line, and as it was the lowest plumbing fixture in the home, the clothes washer had literally filled up with sewage. Since this old clothes washer included a pressure switch that automatically turned on the washer when it sensed that the tub was filled, the washer had not only received backing up sewage, but had begun agitating it in the middle of the night.

Further investigation showed that sewer backups were notorious in the neighborhood, and that this home lacked a sewage backflow preventer at the home's connection to the sewer line. The home suffered from

• A village sewer line that was prone to backups
• No backwater prevention valve protecting the home
• A cross-connection that improperly connected the clothes washer to the home's drain piping without an air gap. (See CROSS CONNECTIONS, PLUMBING).

Question on basement flooding due to sewer line backup:

I had a sewer backup into my home again yesterday at a basement toilet. Our main line has a sewer back-up flap [a wastewater check valve or backwater valve].

The main sewer line check valve works fine when sewer is full from a very heavy rain in a short time. But yesterday we had 60 cm rain in 30 minutes. I had back-up valves on the sink, vanity, shower,clothes washer (drains).

The only place where backup occurred is the basement toilet. I managed placing a ball of rags into the toilet and applying pressure that stopped the water.

Our backup was actually clean water from a flat roof draining into the sewer venting pipe. This is a duplex home.

Is there such a thing as a soft plastic or other material filled that would take the shape of the toilet and prevent water coming back up as overflow. Like I did with a ball of cloths, and a brick wrapped in plastic. It did the trick in an emergency, but it's not practical. - (Anonymous by request)

Answer:

The advantage of installing a main sewer line backup prevention valve is that this device will avoid having to plug multiple drains in the home, and the valve, basically a big check valve, is always in place - you don't have to do a thing to get it to work.

If you are having plumbing or sewer line drains back up, including at the toilet, then either your main sewer line check valve is not working, or your backup is occurring (as you suspect) because water or wastewater is draining into your in-house building drain/waste/vent system before or ahead of the main sewer drain check valve. While you could install another check valve at or near the basement toilet waste line, it makes more sense to install just one such valve to protect the entire building and to make sure that one is working properly.

Stuffing a rag or any other temporary "block" into a toilet or other drains is not the best approach to this problem. Not only can it be unsanitary and a health risk in some cases (see SEWAGE PATHOGENS in SEPTIC SLUDGE), but also, who is going to stuff drains when flood conditions occur and no one is at home?

Install a Main Sewer Line Check Valve or Sewer Cutoff Valve or Make Sure Installed Valves are Working

First you may want to have your main waste line backup check valve inspected - if the sewer line is backing up from the street into your home, your main sewer sewer backup valve (waste backwater valve) or a flood guard valve is not working properly it won't protect from flooding from storm drainage or sewage backups.

Here is a Check Valve Maintenance Guide from the City of Ann Arbor, MI.

Mainline Backflow Products, a producer of sewer line check valves and related products, informs us that:

Many municipal Building Codes require you to have a backwater valve if your plumbing fixtures are below the top of the first upstream manhole on your street.  A properly operating backwater valve allows flow to only go in one direction (out), preventing wastewater from entering your building during regular sewer system maintenance or accidental sewer system backups.  To find out if you have or need a backwater valve, check your plumbing plans or consult with your builder or a professional plumber.  Remember, if sewage backs up into your home, the cost to repair damages and clean up the mess will be well high than the cost to install a valve.  Laws allow that towns and municipalities cannot be held liable for damages when a backwater valve has not been installed by a property owner. 

The City of Chicago and folks writing about Chicago sewer backups offer advice about avoiding sewer backups including the use of basement floor drain standpipes:

A stand pipe is a short section of pipe that when screwed into the basement floor drain will prevent water from coming in through the drain. However, if there is enough pressure in the sewer system, the sewage will rise through the wash machine drain connection, utility sink, and basement bathroom fixtures. A stand pipe does nothing to relieve the pressure in the sewer system, and can cause the sewer lines to crack or break under the foundations. When this happens, the sewage will cause cracks in the basement floor, and may come through the basement walls. If there is enough pressure, the basement walls can collapse, or the foundation can "float" out of its hole. In the worst case, the entire house can collapse into the basement. Because of these dangers, stand pipes and other methods of blocking the drains ARE NOT RECOMMENDED!

Don't Route Roof or Surface Drainage into the Sewer Piping System

Second, you should disconnect your roof drainage from the sewer piping system entirely, routing it to a nearby storm drain, or to the ground surface (at least 12 feet away from the building and to a location that drains away from the building to avoid basement flooding).

If connecting roof runoff drains to the sewer system is actually permitted in your neighborhood, try changing the drain connection to one that is downstream from your main sewer line trap and check valve.

By the way, in some communities it is illegal to rout roof runoff into the sewer piping. Doing so significantly increases the wastewater volume load on the municipal sewer treatment system so severely that during a storm the sewage treatment plant simply overflows, dumping raw sewage into nearby rivers or waterways.

Keep your Drains from Clogging & Unblock Slow or Clogged Drains

A clogged building drain can also lead to a sewage backup or toilet overflow even if the main drain is properly protected from sewer line backups. Flushing needles, diapers, paper products, sanitary products, and grease into drains is always a bad idea.

We discuss some of these items for homes served by private septic systems at NEVER FLUSH INTO SEPTICS. It's a good idea to keep those same items out of drains connected to a municipal sewer as well.

See CLOGGED DRAIN DIAGNOSIS & REPAIR for details about slow or clogged plumbing drain diagnosis, prevention, and repair.

Other Floor Drain Check Valves to Prevent Basement Floods

In addition, or sometimes instead of a main sewer line check valve, flood guards are often installed in individual floor drains for drains up to 4" in diameter. But if a main sewer drain check valve is installed and we are not draining roof runoff into the building drain piping, these should not be needed except on floor drains that connect not to the sewer piping but to a separate storm drain system.

Questions & Answers regarding this article

Questions & answers about backflow preventer valves, sewer backups, toilet drain backup prevention and sewer line backup prevention.

Question: Is there a plug for toilets that will prevent sewage backups into my basement?

Quick question, when it rains hard where I live our basement toilet backs up with water. Is there a plug of some sort I can put in it to stop this from happening.

Something like a shower plug but that would work in toilets. Thank you for your time. J.P.

Reply: How to plug or seal off a basement toilet and the buiding sewer line against sewer backups

A competent onsite inspection by a plumbing expert who is familiar with sewer backups usually finds additional clues that help accurately diagnose a problem such as an improper house drain installation, other sewer backup risk points such as basement floor drains or sinks, even washing machines, or the need for a check valve or backflow preventer valve at your home main drain.

How to plug or seal off a basement toilet against sewer backups - temporary toilet seals are unreliable and risky but here are some suggestions for preventing sewage backing up through a toilet on the building's lowest floor.

How to plug a toilet drain against sewer line backups: toilet drain test plugs

We don't know about a functional plug that fits in a toilet bowl and that reliably seals any toilet bowl shape against sewer backups.

As we describe here, there are however plumbing drain test plugs designed for all sizes of drain piping including ones commonly used to close off a toilet drain opening when no toilet is installed. And one type of these might work to seal some toilet bowls, depending on the toilet bowl shape and dimensions.

Typically a toilet drain piping itself is 4" in diameter and can sealed easily using a 4" expanding test plug. But sealing the drain inside a toilet bowl against sewer backups is a different matter. First the toilet bottom opening is not round, so a plumbing drain test plug may not seal the drain reliably; second forcing a plug into the bottom of a toilet risks cracking and ruining the bowl; third, using something makeshift (a ball of newspaper or loaf of bread) risks flushing a hard-to-clear blockage down the drain; third, even if we can plug the basement toilet against sewage backups,

Nylon or metal based expanding plumbing drain test plugs using rubber, silicone, neoprene, nitrile, or vitron flexible seals are devices that employ a screw and compression plate to permit a plug to be inserted and expanded to seal a round drain opening.

Plumbing drain test plugs used for testing plumbing drains for leaks (openings are plugged and the drain system is pressurized) are available from most plumbing suppliers.

But most plumbing drain system test plugs such as Pipestoppers™ won't work nor seal properly in openings that are not round. [4]

Flexible or inflatable pipe plugs may fit some toilets

An exception that might fit some toilet bowls and permit plugging an in-place toilet against occasional sewer backups are inflatable plumbing test plugs such as the Petersen line of inflatable plumbing test plugs and the Test Ball® Inflatable Plumbing Test Plugs produced by Cherne Industries. [5] [6]

Watch out: plugging a basement toilet or toilet drain might stop sewer backups that have been flowing up and out into the building through one or more toilets found on its lowest level. But if other drain openings are present, the rising pressure from a sewer line backup may simply find the next higher drain opening (bath tub, sink, shower floor, even washing machine). That's why we recommend the alternative sewer backup prevention steps listed

Abandon the basement toilet to prevent sewer line backups into the building?

If your home includes a basement toilet that is a source of sewer backups, and if there are no other low-building drains that will assume that role if the toilet is eliminated, we suggest you consider removing the toilet completely, abandoning its use, and plugging the toilet drain line at floor level.

But if the basement toilet is needed and/or if there are simply other drains that will become the sewage backup and entry points if the toilet is removed, abandoning the toilet doesn't make sense.

How to use backflow prevention valves, backwater valves, or main drain check valves on the building drain protect against sewer backups

That said, our last suggestion is the best solution - a check valve (properly referred to as a backflow prevention valve or in some areas a "backwater valve") can be installed on the main building drain can prevent sewer backups through the toilet when the area sewer lines are flooding.

Install a flood alarm or backflow preventer valve (backwater valve) integrated flood alarm

If your home is subject to frequent risk of flooding or water entry or sewer backups, look into a flood alarm that can be installed along with the backflow preventer valve on your main building drain.

Alarms are available that sense water on the basement floor, indicating the beginning of water entry and provided someone is at home, giving time to investigate and take action.

But when discussing sewage backups through lower floor drains or toilets, we refer you instead to a somewhat different product such as the Rialco™ flood alarm [3] that is integrated into your backflow preventer, informing you when that special check valve has closed against a sewer backup.

By installing a replacement waterproof cap on the backwater valve installed at the main building drain, the modified back-water valve cap permits connection of the Rialco flood alarm sensor tubing to a port that will inform the alarm that the backwater valve has been activated. Thus the building owner or occupants are informed of sewer line flood conditions as well as of the fact that the valve is working.

Besides backflow preventers, other types of check valves used on building plumbing and heating systems are discussed at CHECK VALVES.

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SEPTIC SYSTEM INSPECT DIAGNOSE REPAIR

SEPTIC BACKUP PREVENTION
  SEPTIC BACKUPS During Heavy System Use
  Sewer Backups - Flooding or Sewer Main Backups
SEPTIC BACKUP REPAIR

SEPTIC TANK PUMPING PROCEDURE
SEPTIC TANK INSPECTION PROCEDURE
SEWAGE BACKUP TEST & CLEANUP
SEWAGE & SEPTIC CONTAMINANTS
SEWAGE CONTAMINATION in buildings
SEWAGE CONTAMINANTS in FRUIT / VEGETABLES
SEWAGE EJECTOR / GRINDER PUMPS
SEWAGE NITROGEN CONTAMINANTS
SEWAGE PATHOGENS in SEPTIC SLUDGE
SEWAGE PUMPS
SEWER BACKUP PREVENTION
SEWER GAS ODORS
SEWER LINE REPLACEMENT

TOILET REPAIR GUIDE

TOILETS, DON'T FLUSH LIST
TRAPS on PLUMBING FIXTURES
WATER SUPPLY & DRAIN PIPING
  CLEANOUTS, PLUMBING DRAIN
  CLOGGED DRAIN DIAGNOSIS & REPAIR
    FIRST SIGNS of DRAIN CLOGGING
    DRAIN vs SEPTIC
    BLOCKED DRAIN?
    DRAIN DRAINFIELD DIAGNOSTIC TABLE
    BLOCKED DRAIN REPAIR METHODS
    PLUMBING DRAIN NOISE DIAGNOSIS
    PLUMBING DRAIN NOISE REPAIR
  CLOGGED SUPPLY PIPES, HOT WATER

• Thanks to reader - (anonymous by request) for discussing alternative preventive measures to stop basement drain and toilet backup prevention - July 2010
• Chicago, IL. Xpert Flood Control, the Causes and Prevention of Sewer Backup, web search 07/10/2010, original source: http://www.floodexperts.com/backup-prevention/ This author also discusses overhead building sewer drains:
  An overhead sewer system can eliminate all but the worst backup problems. In such a system, all of the waste from your house is collected in a well in your basement floor. This waste is pumped up to ground level and out of the house in a replacement sewer line. Near the street, the replacement sewer line is drained down to the municipal sewer line. As long as the sewer pressure is not enough to push water up to ground level, sewage will not be able to flow back into your basement. If the water level at the street drains is higher than the overhead sewer pipe, the sewage will flow back into your basement, and the basement can be filled.
• Mainline Backflow Products - Backwater Valve Supply Co., Akron, OH, Tel: 330.836.9393, Email: Help@Backwater-Valves.com, website www.backwater-valves.com/Backwater-Valve-Diagram.asp has a good sketch that is their basis for recommending when a sewer backup prevention valve is needed. Web search 07/10/2010 - original source: www.backwater-valves.com. Quoting from the company:
  Many municipal Building Codes require you to have a backwater valve if your plumbing fixtures are below the top of the first upstream manhole on your street.  A properly operating backwater valve allows flow to only go in one direction (out), preventing wastewater from entering your building during regular sewer system maintenance or accidental sewer system backups.  To find out if you have or need a backwater valve, check your plumbing plans or consult with your builder or a professional plumber.  Remember, if sewage backs up into your home, the cost to repair damages and clean up the mess will be well high than the cost to install a valve.  Laws allow that towns and municipalities cannot be held liable for damages when a backwater valve has not been installed by a property owner. 
  Classification: Type I – intended for use in horizontal pipe runs to floor drains, building drains, sewers, holding tanks, etc.
  Application: Backwater valves should be used in building drainage systems whenever a risk of flooding due to sewer surcharge, back up, or failure exists.
  Backwater valves must be installed to ensure access for inspection or maintenance.
  Periodic inspection is important to maintain satisfactory performance of the backwater valve.
  The building owner must maintain and keep backwater valves in proper working order. 
• Check Valve Maintenance Guide from the City of Ann Arbor, MI. , web search 07/10/2010, original source: http://www.a2fdd.com/Documents/maintenancedoc_checkvalves.pdf
• [3] Rialco Inc., the Rialco Flood Alarm, web search 10/03/2011, Dean & Amber Taylor, Phone: 416 733 7758, Fax: 416 733 2918 Rialco Inc. 237 Spring Garden Ave, Toronto ON M2N 3H1 Canada, original source: http://www.rialco.com/ Quoting from the company's website:
  The Rialco Flood Alarm was created after a Canadian inventor flooded several floors of his downtown  condominium by leaving his bathtub running to answer a phone call.  Since that incident, thousands of people world-wide have benefited from the monitoring and early detection capabilities of the Rialco  Flood Alarm.
• [4] Pipestoppers™ produces test plugs for pipes sized from 1/2" up to at least 6" in diameter.
• [5] Petersen Pipe Plugs, produced by Petersen, include inflatable and flexible drain test plugs that may work in some toilet bowl shapes. Tel: 1-800-926-1926 Email: sales@petersenproducts.com, Petersen Products Co., P.O. Box 340, 421 Wheeler Avenue, Fredonia, Wisconsin 53021-0340 USA.
• [6] Test Ball® Inflatable Plumbing Test Plugs for pipe diameters up to 10" employ a flexible inflatable bladder that may work in non-round openings including some toilet bowl openings. Test Ball® plumbing drain test plugs are produced by Cherne Industries, a division of OATEY S.C.S. Contact: Cherne Industries, 5700 Lincoln Drive, Minneapolis, MN 55436, Email: info@cherneind.com, Phone: 800-843-7584 Fax: 800-843-7585
  

• The Septic System Information Website home page for this topic
• Septic Systems Inspection, Testing, & Maintenance- online textbook. Detailed how to inspect, maintain, repair information


• The Home Buyer's Guide to Septic Systems
• SEPTIC TANK PUMPING SCHEDULE When, Why, How to pump the septic tank
• Septic Tank Pumping Procedure step by step photo guideline of how to pump and clean a septic tank - septic tank care
• Tank Location - How to Find the Septic Tank, how deep will the cover be, how to document its location
• Home & Outdoor Living Water Requirements
• Septic Tank Capacity vs Usage in Daily Gallons of Wastewater Flow, calculating required septic tank size, calculating septic tank volume from size measurements
• Septic System Design Basics: Choosing Septic Tank Size, Absorption System Size
• Table of Required Septic & Well Clearances: Distances Between Septic System & Wells, Streams, Trees, etc.
• Ten Steps to Keeping a Septic System Working, suggestions from the U.S. EPA, edits and additions by DJF


Pennsylvania State Fact Sheets relating to domestic wastewater treatment systems include

• Pennsylvania State Wastewater Treatment Fact Sheet SW-161, Septic System Failure: Diagnosis and Treatment
• Pennsylvania State Wastewater Treatment Fact Sheet SW-162, The Soil Media and the Percolation Test
• Pennsylvania State Wastewater Treatment Fact Sheet SW-l64, Mound Systems for Wastewater Treatment
• Pennsylvania State Wastewater Treatment Fact Sheet SW-165, Septic Tank-Soil Absorption Systems
• Document Sources used for this web page include but are not limited to: Agricultural Fact Sheet #SW-161 "Septic Tank Pumping," by Paul D. Robillard and Kelli S. Martin. Penn State College of Agriculture - Cooperative Extension, edited and annotated by Dan Friedman (Thanks: to Bob Mackey for proofreading the original source material.)
• ...

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• Typical Water Tests & Fees this water test fee schedule applies when testing is combined with other onsite building inspection services
• Water pump and pressure tank repair diagnosis & cost an specific case offers an example of diagnosis of loss of water pressure, loss of water, and analyzes the actual repair cost
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• ...