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How Do I Know if My Septic Tank is Leaking?

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Signs your septic tank may be leaking

Unfortunately there are no easy-to-spot signs of a leaking septic tank; most homeowners will not know their septic tank is leaking unless it is opened and pumped out. This may be done for routine maintenance or may be done during a real-estate inspection.

Where leaks occur

Most septic tanks are installed in a top and bottom section, and it’s where these two sections meet that we most often find leaks. The seam of the tank is usually several feet below the surface of the ground, so there are usually no visual signs over or around the tank that indicate excessive moisture.

Two indicators of leaks

Low liquid level

The tank should always be filled to the outlet pipe (about 8-12 inches from the top of the tank). All tanks should be watertight, so the wastewater inside should still be there several years later if the home is left unoccupied.

If a home is occupied, a leaking tank may not be detected because the occupants are constantly adding water to the system, so the liquid level may be normal when the tank is opened. However, when a house is vacant, it allows time for the liquids to seep out and a leaking tank may be more apparent.

Liquid flowback

This is found most often when a house is occupied and the liquid level appears to be normal (not low) — but as the liquids are pumped down in the tank, water starts seeping into the tank because the soil on the outside of the tank is saturated and holding water.

Testing for leaks

If a house is occupied and the liquid level is low, it is a good indicator that the tank is leaking. If the house is unoccupied, a leak can be verified by filling the tank to its normal liquid level, waiting 24-48 hours without running any water inside the house, then re-checking the liquid level. If the liquid level drops, it verifies the tank is leaking.

Leaking tanks are hazardous

Although the homeowner may not experience any conventional “problems” with the system (such as a backup in the house or moisture over the yard), a leaking tank is considered an environmental hazard.

There is no guarantee that sealing a leaking tank will fix the problem (or fix it for long) — therefore it is usually recommended to replace a leaking tank. Depending on the age of the system and local regulations, replacing a septic tank may require replacing the entire system.

Want to learn more about septic tanks and how they work? Download a free copy of Understanding and Maintaining Your Septic System.


31 thoughts on “How Do I Know if My Septic Tank is Leaking?

    • Hi,
      It doesn’t sound like that is due to a leaking septic tank. Are you having any backup in the house? My suggestion would be to contact a plumber if you aren’t having any backup in the house. If you are having backup in the bathroom, a plumber could also help determine if your problem is due to your septic system or the plumbing. Hopefully its nothing major!

  1. Okay, my boyfriend and I bought a house in April 2013. The previous owners had to install a new tank before we moved in. So the septic tank isn’t even two years old. Today, Feb. 19, 2015 we found out it is leaking. Now, a company came in and dug a hole for another company to come in and drop the tank. There is a hole that sunk in about two feet off the house. We found it, because the dogs would go over and dig in it a little. So we suspected there was a problem, when I flushed the toilet my boyfriend said he saw air bubbles. We called the septic tank people they said it’s not their problem it’s the people who dug the hole. We have the health department check on our tank, how come they missed it? I don’t want to get screwed with a huge bill. Who is responsible for this?

    • Wow! I’m so sorry to hear about your situation. Without actually seeing what is going on, there is no way for me to tell you who is responsible for the problem. Sometimes after tank installation, natural settling can occur around the tank, which is resolved by bringing in more dirt. However, seeing air bubbles makes me think it may be a different issue. The problem is, you have two contractors (the digger and the tank installer). Our company does everything as a package (digging, installing, etc.) which helps to avoid the blame game if there were any problems. I suggest having a 3rd party who would be non-biased to assess the situation and document with photos what they find so that IF there is someone at fault, you can present your case. I wish you the best of luck!

  2. I have a phorid fly problem in my basement. They seem to be coming from a pvc pipe sticking out of the floor near the furnace. This has been there since we moved in 17 years ago and it is not used for anything. How do I know if there is a leak in my septic system causing them to make their way into the basement? These flies come every summer now for the last 7 years and leave as soon as it gets cold outside in October. We just figured out that they might be coming from this pipe in the floor. Otherwise, we do not have any signs that we have a leak.

    • Do you know for sure what the pipe sticking out of the floor is for, or what it’s connected to?

  3. Hi all, just moved into a house that has a septic above the house (elevation) so I have a pump. Every time the pump goes water rises just outside the foundation then seeps back into the ground. Is this just a broken pipe? Or something bigger?

    PLEASE HELP! MY WIFE IS DUE IN A WEEK!!

    • I would definably call a professional right away! This surfacing water is not normal and likely will not resolve itself. Especially with a baby on the way, I’d get it fixed today!

  4. My system is uphill from the discharge sprinklers. Water seeps out after the discharge I assume due to gravity fed pressure. I just replaced the heads with some that specifically had check vales and they still leak…….I have small swamps around each head that is driving us nuts!! Any suggestions…??? Thanks, JW

    • It’s always best to consult the installer or your service provider, but this is the first thing that comes to mind is that sounds like you may need to do something to break the vacuum in the pipe. If there is no vacuum break in the pump-line in the pump tank the water can siphon through the pump to the distribution heads after the pump has turned off until the water level reaches the pumps intake level and breaks vacuum. Typically there is a sample valve located on the pump-line inside the tank. If so you may crack it open in order to allow it to suck some air after the pump turns off which should provide the vacuum break. If there is no sample valve a small 1/16” to 1/8” hole can be drilled in the side of the pump-line inside the tank to serve the same purpose.

  5. I am renting a home with a septic tank, yesterday we noticed a small spot of some dark liquid coming from the ground, today that liquid has over tripled in size. I msg my landlord but no response. I have never had a septic like this, what do I do?!?

    • It sounds like the drainfield is not accepting your wastewater, causing it to backup into the tank then surface over it. Check for leaking toilets, dripping faucets, malfunctioning water softener, etc. that might contribute to flooding out the drainfield. Pumping the tank can temporarily relieve the seepage over the tank, but as soon as the tank re-fills (a few days to a week), the same thing may occur. A local and licensed septic installer can guide you further as to what would be needed to correct the problem.

  6. We are buying a 100 yr old house on contract and haven’t quite been there a year yet. About 3 weeks ago I’d noticed some water in one of the rooms of the unfinished basement, where the furnace and water heater sit. I thought my water heater might be leaking but couldn’t really see any place where it would be leaking. Fast forward, go down to the basement and there’s probably 5″ of water down there spreading to all the rooms. We bought a utility pump and have been trying to pump the water out, but it slowly returns to a constant level of about an inch in that room I mentioned earlier. I see no leaking pipes and I don’t see where the water can be coming from where it seemed to originate. I am very worried though because I smell sewage and am hoping it’s not an issue with the pipe or septic tank leaking and seeping into the basement. We were told the septic was replaced about 2 years ago and can’t afford to have the tank replaced….please advise.

    • We don’t have basements here in Texas, so I’m unfamiliar with how all the plumbing works with basements. Pretty much everywhere requires permits for new septic systems – have you tried contacting the installer or permitting office to obtain installer information? Having a plumber or the septic installer come out would be the best option – it may be a process of elimination. Unfortunately, without someone doing actual diagnosing in person, there’s not a lot to advise on. I hope you can get it figured out!

  7. Hi, about a week ago we opened the lid to the septic to add the root crystals to it. It was full to the lid with liquid almost pouring out. After about 2 hours it resided about a foot and a half and has stayed there. Now there is a mushy patch of our yard. We have no oder inside the house. No problems with draining or flushing. I’m curious if maybe out tank is full?

    • In general, you don’t want to add root killer to the septic tank – if you use any root killer, it should go in a cleanout past the tank to avoid harming the tank and/or the bacteria in the tank. However, the level in the tank should never be full to the lid (probably un-related to the root killer). An “overfull” tank usually is an indication that the drainfield is not accepting/absorbing the amount of water introduced into it. If the level in tank has resided, this sounds like the normal operating level. However, a mushy patch over the drainfield would be another indication that the drainfield is not allowing the wastewater to percolate. At a minimum, keep an eye on both and see if it has to do with periods of heavy wastewater usage. Also, check for leaking faucets, running toilets, malfunctioning water softener, etc, as they could cause a septic system to flood out.

    • I was doing back to.back loads of laundry. A few days ago I did back to back, heard my toilet gurgling and water was going down the toilet and water was coming out the top of the manhole onto the yard. I haven’t used much water the last few days and the water in the manhole is down about 3-3.5 feet. A lot lower. So I’m thinking the mushy patch is from too much water all at once and just not noticing cause I don’t go outside when I do the laundry. and to space everything out when using water.

  8. We just had a concrete septic tank put in.. it looks like there are some cracks in it..so we filled with Jose water about 6 inches.. there are no toilets hooked up to it as the house is being built now.. anyway we checked the level of water with a marked stick… the next morning about 12 hours or so we checked and the water dropped 2 to 3 inches below the line … we called the guy that installed it and he said because it’s a new concrete tank they absorb water at first… is this true?

    • Well, that’s a first time I’ve heard of a new concrete tank absorbing water. I would do your test again and take pictures of the filled level and the low level. Or, fill it a little higher than before and check it over a few days (marking the level each day). You might want to call other septic installers and ask them, so hopefully, you have more of a consensus of the same answers.

  9. my dishwasher was leaking blue fluid in the kitchen and in the basement where the water lines are. Is that from the discharge? Is septic fluid leaking?

  10. We are selling our house. We had our tank pumped and the guy said it was at a normal water level. A week later our buyers had the tank inspected and their guy said the water was too low. He came back 5 days later and said the level hadn’t risen enough for a family of 4. Now, my husband has been away on business, I work full time and my kids are at school so no one is really home for there to be a lot of water usage. Could there be a leak if only 1 1/2 weeks ago the tank was actually pumped???

    • This is just one of the reasons the tank should not be pumped before the septic inspection, but lets deal with your situation. Right now, your situation is hard because you don’t know exactly how much water you are using, and neither does the inspector that said it hasn’t filled up enough yet. Usually, a family of 4 In most cases, the best way to verify if the tank is leaking: fill the tank to its normal level (to the outlet pipe) measure the liquid level, then wait 24-48 hours (but NO water can be run inside the house during this time – so you would have to leave the house for a day or two – checking the water meter can help verify that no water was run between filling and re-checking), then re-check the level and re-measure to determine if the level has dropped. Although this may not be ideal (to leave the house for a day or two), it’s the best way to verify if the tank is leaking or not. Also, you could check your water bills (if you pay for your water vs. being on a well) and figure out how many gallons of water your family uses per day over an average of several months (take the total number of gallons billed for, then divide it by the number of days in the billing cycle – and do this for several months of past bills to get an overall average). Typically, ON AVERAGE, a septic tank may only take a few days to a week to fill up. However, I have a family of 4 as well. We use 166 Gallons Per Day on average. If I have a 1250-gallon tank, then it would take about 7.5 days for my tank to fill (on average). If you can find out what size your tank is and do the math, that MAY be an indication as well. Best wishes!!

  11. I sublet a shed on a property that has 7 people, I noticed moisture seeping up from the ground near my front door, even when its not raining this spot is wet. Over the past 2 years it has gone from a palm sized spot of moisture to a 9ftx3ft wet area so bad we don’t walk there because its always muddy. It does have a sewage smell but not all the time. We notice when the shower is used, laundry washed, and if the toilet is left to run we smell it. According to the roommates its not been pumped for 5 years that they know of, system is the original one from 1976. They do not believe us when we bring our concerns to them. Discrediting our arguements. Is there some way to get the soiled tested to see if I’m imagining anything? What can I do?

    • Try calling around to local labs to see if they can test the soil. If its bad enough, see if you can collect some liquids to be tested (which would probably be ideal). Digging to find the source of the surfacing water may also help in determining/verifying the cause. Take caution when digging though.

  12. My septic alarm keeps going off. To my knowledge the pump is not in the basement, I can’t find it anywhere. I’m coming up short with any sort of troubleshooting and it’s a Sunday night. The alarm has been going off relentlessly for hours. Not sure what to do but I’m panicking.

    • Without knowing what your pump is for (how your system is set up), its hard to give advice on how to diagnose or at least look for major immediate issues. Check for a silence button to silence the alarm, reduce your water usage in the house, and call a service company when they open to help you out. Best wishes!

  13. I had my septic pumped 3 years ago and its time again, I called the same guys but this time I was told the leech line would have to be moved when they pumped it 3 years ago, and they left the whole area open, anybody could fall in, is this goid business?

    • I’m a little confused, can you clarify what area was left open and why? And why do the leech lines need to be moved just for pumping?

  14. We had serval stoppage so we call the plumber they came out and said our septic was full ( our septic lid is under dirt so we dug out the lid so it can be pumped )so we called and had them pumped out our septic when they did they told us that our leech bed was flooded and to not use a whole lot of water so we did this. We never replaced the dirt on our septic lid because the gentleman said we might have a problem with our leach field, because it was flooded ( we also had just spent three weeks of getting a lot of rain so I know that didn’t help ) we’ve not had any puddling of water anywhere but we noticed because we do not filll the dirt back on the lid, water was backing up a little bit out of the lid a couple inches would go down every day but would come back every day as well, is this normal I don’t want to call the septic guy back because he will charge me $250 to come back out and tell me if I just need to put the dirt back on the lid or if it’s normal level of the water in the septic now. we are not having any more stoppage issues or slow drains or anything like that.

    • The normal operating level in most tanks is about 8″-12″ from the top of the tank. The fact that the liquids are seeping over/out of the top of the tank is usually indication that your absorption area is not able to accept the amount of water you are using. Sometimes the liquid level can fluctuate as periods of non-water-usage may allow the absorption area to slowly let the liquids percolate. Check for dripping faucets, running commodes, malfunctioning water softener, etc. to rule out any extra water entering the system unnecessarily.

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