Photo of a leak into a septic tank at the sewer line connection (C) Daniel Friedman Septic Tank Back-Flooding FAQs
Q&A on how to diagnose & repair septic tanks with abnornal sewage levels

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Septic tank flooding or back flooding questions & answers:

Questions & answers on the causes and cures for flooded or back-flooded septic tanks.

Backflooding means that water or wastewater is flowing backwards into the septic tank from a soakbed or drainfield or from surface runoff.

We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

Septic Tank Flooding & Back-Flooding: Why it is important to diagnose & fix water leaking into the septic tank

Septic tank diagram shows normal sludge and scum thicknesses[Click to enlarge any image]

These questions & answers about flooded or back-flooded septic tanks were posted originally at SEPTIC TANK BACK FLOODING - be sure to see that article.

On 2018-04-12 by (mod) - investigate a wet spot in the drainfield

Yes, Scott, a blocked or broken line, or a backup leaking at an inspection port, or (worst news) a clogged, failed drainfield.

I would dig at the wet spot, with care, to find the conditions there in the actual drain field piping - that'll be diagnostic.

Use the "Add Image" button next to the Comment button to attach photos of what you find and we can comment further.

On 2018-04-12 by scott

What would cause my drain field to leak into my yard the leak is located about 20 ft from tank, I was thinking a broken line

On 2018-02-28 by (mod) - When it rains water from the septic lines runs back into the tank


I am genuinely sorry to be the bearer of bad and expensive news, but a septic drainfield that floods from ground-water in a level area is probably improperly designed and needs significant revision.

The bottom of the drainfield trenches needs to be at least 24 inches above the seasonal high water table - that can mean a raised bed septic or mound septic design (search for those phrases to read details).

Sometimes an intercept drain around the fields can carry off ground-water and leave fields working but that works best where there is some slope and some hope.

I'm doubtful that it'd work in an entirely level area as water may just come up under the intercept drain and into the septic area.

On 2018-02-28 by Buddy Cromer

I have flat ground. When it rains for days the ground get socked and the water from the lines runs back into the tank. Is there anything that can be done?

On 2018-02-24 19:12:39.660123 by (mod) -

No, Terry septic tanks don't use a backflow valve.

You need some on-site help to see if the fields are saturated or blocked - start by checking in the D-box.

Also look for surface or ground water leaking into the septic tank

On 2018-02-24 17:56:29.668397 by Terry

Does the tank have s back flow valve?

On 2018-02-24 17:55:07.398914 by Terry

High waters recently septic tank keeps filling with water?

On 2018-02-12 19:43:08.823818 by (mod) -


Back-flowing into the septic tank, if it stops quickly - minutes or less - could be a simple blocked line.

But if it continues longer the fields are most-likely saturated - which your description suggests is the case.

Given that the curtain drain hasn't fixed the trouble I suspect

1. the curtain drain doesn't go deep enough or lacks capacity to keep extraneous groundwater out of the septic fields
2. the fields are basically in failure regardless (or both)

You may need to go to a raised bed or mound septic. That does not mean just adding soil over the existing fields. That won't work and will block oxygen. Instead it'd be a new elevated pipe network in a mound.

On 2018-02-12 17:21:48.290355 by tbv

we have a two concrete box septic system for a very large house. last spring and recently our drain field (back yard) has been back flowing into the tank which holds the gray water. This tank subsequently backs into the primary tank causing it to become full.

During pumping of these tanks we can witness water flowing back into the outlet hole. Our backyard during heavy rains in the spring becomes wet and soggy. To remediate the problem we put in a curtain drain last spring. It helps and we can see water flowing out of curtain drain but hasn't solved the problem.

What to do next? Any suggestions would be appreciated.

Back yard is flat and I'm told adding soil to it puts your leach field lower than ideal and makes it harder to incorporate evaporation, wind sun to dry leach field.

On 2017-09-19 02:54:46.994934 by Peggy

My septic tank is not completely in the ground. Should it be

On 2017-05-07 12:52:52.388741 by (mod) -


1. Give a call to your septic pumping company to have the tank pumped: that will stop the immediate risk of a costly sewage backup into your home3 and will give you 1-3 days to find out what is the real problem. (After that the tank will be full again).

During pumping there is more information to be learned - the condition of the tank, tank baffles (bad baffles = clogged incoming lines or clogged drainfield), backflow into the tank from its outlet means the soakaway bed is flooded, failed.

Read with care the article above on this page about septic tank flooding: causes, implications.

2. Diagnose the cause of backup in the septic tank; a broken or clogged pipe can be repaired.

Flooded or failed septic drain field will require replacement, or at the least, direction of surface runoff or groundwater away from the fields.

On 2017-05-06 22:46:27.103401 by Nancy

What do I do when the water starts running out of the top of my septic tank? septic tank

On 2017-03-28 18:10:52.061370 by (mod) -


With the
Watch out: warning that leaning over an open septic tank inspection cover can expose the observer to methane gas, fainting, falling into the septic tank, or other hazards

with that arm-waving stuff out of the way:

Find the septic tank

Open the inspection cover over the tank outlet

Look at the level of sewage in the tank:

- if waste is at the top of or flowing over the top of the outlet baffle or tee then yes, waste is not leaving the tank

That can be traced to a blocked waste line out of the tank, a flooded D-box, or a flooded or failed drainfield

On 2017-03-28 12:49:15.929366 by Sharon Powell

We just had our tank cleaned out in Jan. and our septic tank has started backing up again, it is a 1k gal. tank with a curtain drain. Hubby seems to think the water isn't going out of the tank. Any suggestions?

On 2016-10-25 15:34:44.293790 by (mod) -


Some excavating is needed to explore the problem.

First you want to find the septic tank cleanout lid and have your septic company open the tank to inspect the sewage level in the tank. If the tank is back-flooding then I suspect a blockage or failure at the tank outlet or drainfield.

The tech will perhaps next have you run water or flush toilets to see how waste flows into the septic tank and to inspect for leakage around the tank inlet.

We don't want sewage leaking OUT of the septic tank and we do not want ground water leaking INTO the septic tank either as that'll flood the system and drainfield and means septic system failure too.

If the problem is simply ground water around the tank and if the septic system is working, you can defer the cost of connecting to sewer by directing groundwater away from the tank and sealing the tank inlet and outlet piping at the tank wall if they are leaky.

On 2016-10-25 01:32:19.254850 by Beth

We are having water pooling around the pipe entering the tank starting at three feet from the house.

The pipe takes a sharp turn downwards to about three feet than veers to the left than into the tank. Since some of this pipe has been covered by a concrete patio (done before we bought the house) we haven't exposed the whole pipe.

We've gotten all kinds of possibilities including the tank needs pumping, the pipe is broken going to the tank, to the lid could be crushed.

There is not wetness in our drain field or anywhere else except around the pipe. Can this be fixed if it is the pipe? Of course the township wants us to hook up to the city sewer but that would cost was thousands. What do u suggest

On 2014-07-08 00:20:40.398610 by (mod) -

Anon, the next point to check is the distribution box. Look for flooding there. Look at the flow of effluent into all the drainfield lines. Indeed the field may be shot but lets make sure.


(July 7, 2014) Anonymous said:

Water lvl in septic tank below effluent. Water did not drain back when pumping. inspector said he saw water in 5 foot length of pipe via video. Pipe goes into elbow then turns down into septic trench. He said we have a Malfunction and will have to replace entire absorbtion field to a tune of 30,000.


Anon, the next point to check is the distribution box. Look for flooding there. Look at the flow of effluent into all the drainfield lines. Indeed the field may be shot but lets make sure.

Watch out: at FLOODED SEPTIC SYSTEMS, REPAIR we explain how to fix a problem with septic tank or soakbed or drainfield flooding.

But be warned, that while in an emergency we might pump the septic tank, simply pumping the septic tank won't fix this problem and worse, if the back-flow rate into the septic tank is rapid (as it often is) you are simply wasting your money as back-flooding from a drainfield or surface runoff will quickly fill the septic tank again in hours to days.


Continue reading at SEPTIC TANK BACK FLOODING or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see FLOODED SEPTIC SYSTEMS, REPAIR to read suggestions for repairing a flooding septic tank or soakbed system

Or see PUMPING the SEPTIC TANK to continue with the septic tank cleaning & inspection procedure

Or see PUMPER TRUCK OPERATION PROCEDURE where we explain how to spot backflooding during septic tank pumping


See SEPTIC BACKUP PREVENTION for tips to avoid a septic problem during times of anticipated heavy septic system usage.


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SEPTIC TANK BACK FLOODING FAQs at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.


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