Septic Tank Full Of Water Not Draining? (8 Things To Do Now)


If your septic tank is constantly flooding, overflowing, or requires drainage more often than it used to, you likely have a fixable problem. However, the problem can vary quite a bit.

For example, if your septic tank is full after rainfall, you are likely to have a flooded drain field.

On the other hand, if your septic tank is simply filling up too quickly or not draining at all, clogs and damage to the pipes or the tank are more likely to be the issue. 

This article will look at 8 common reasons your septic tank might not be draining. It will also go into common fixes, and what you can do to prevent those issues in the first place. 

8 Reasons Why Your Full Septic Tank Water Is Not Draining

If your septic tank isn’t draining, it could be any of a number of issues. However, the following 8 are the most likely. 

1. Clogs

Clogged septic tanks normally happen when you flush large items down the drain.

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In addition, if you flush things that are not human waste or toilet paper, they won’t break down. That’s even true if you have a garbage disposal.

Even fine bits of waste will collect in your septic tank and won’t break down the same way human waste and toilet paper do. 

In addition, you could have clogs from: 

  • Flushing small contaminants like hair or cleaning clothes over time. They won’t cause a clog immediately but can build up and cause one over time.
  • Flushing harsh chemicals such as bleach and drain cleaner, which could disrupt the bacteria that break down toilet paper and human waste
  • Plants growing in or around the drainage area of your pipes
  • Flushing food with fat in it. This will harden in the cold septic area and attach to pipes and joints. Then, it will bind to any other fats that move past. This can cause large lumps of fat that block pipes. Or, it can narrow pipes, reducing the speed at which your septic tank is able to drain. 

Often, there are only two options to remove clogs from your septic system.

The first is to use a plumbing snake for unclogging the septic tank drain pipe by working out any clogs and breaking up large items. The second is to take the system apart and manually remove large clogs. 

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Once you do, it’s always a good idea to consider if filters, additional bacteria, or other preventive measures are a good idea. 

2. Tree Roots 

If you have trees or large plants growing around the septic tank or the drain field, they can cause significant issues for your septic system.

Here, roots at the drain field will often grow into the open drainage pipes. That makes sense, considering they seek out water and nutrients. 

However, tree roots can also cause significantly worse problems. For example, they can grow under or over your septic tank.

This can cause disruption, tilting, and breakage of the tank. When that happens, roots and dirt can clog the system itself. Or, your system might stop draining altogether. 

Here, it’s always important to keep tree roots as far away from your system as possible. In most cases, you should have root barriers and soil prepared to direct tree roots elsewhere.  

3. Drain Field Issues

If your drain field floods when it rains, your septic system will stop draining. That’s also true if your septic system is installed in a muddy field and floods as well.

It’s often important to do multiple tests before installing your drain field. For example, you should know where the groundwater level is. You also shouldn’t be attempting to empty your septic tank immediately after rain. 

However, if your drain field is flooded, it does explain why your septic tank isn’t draining. The drain field is a series of perforated pipes buried just under the ground.

They allow liquid wastewater, also known as effluent, to flow into the drain field. The solids separate out into the tank, where they can break down naturally. 

If the drain field is waterlogged, the field can’t drain. So, your sewage tank will fill with water and it will back up.

In some cases, it’s good enough to wait for the soil to dry, especially if it’s recently flooded or rained heavily. In others, you might want to check for deeper issues: 

  • Compacted dirt or mud around the drain field. For example, if a vehicle has run over it, the holes in the pipes might be clogged. 
  • Roots or plants growing into the holes in the pipes. You should never have plants growing over a septic tank rain field. 
  • Keep gutter systems away from the drainage field. Gutter water should be directed elsewhere
  • If issues keep happening, you might want to excavate the field and re-fill it with better-draining soil. If your local dirt compacts, or is entirely made of clay or silt, etc., it may be a good idea. In this case, you’ll want to consult with a professional to see if it’s necessary. 

If your septic tank is full when it rains or doesn’t drain after it rains, drain field issues are the most common issue. 

4. Installation Issues 

Your septic tank might not drain properly if it’s been installed improperly. Here, issues can range from how drainage is set up, the angles on the drain field, or even the angles on the drain pipes.

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If the tank keeps not draining, you may want to have it inspected by a professional to ensure that everything is as it should be. 

5. Damage 

If your septic tank, drain pipe, or drain field has been damaged, it could cause flooding.

Here, you’ll have to physically inspect the tank to find issues. Signs of damage include: 

  • Tree roots around the tank
  • Heavy compaction around the tank. For example, if someone drove over the area.
  • The tank is starting to lift on one end or ground has shifted around the tank
  • There is flooding, wet spots, or noticeable green spots between your home and the drain field 

In each of these issues, you’ll have to dig up the septic tank to inspect it and to make sure there aren’t issues.

If there are, you’ll have to replace the damaged part. 

6. Dip Pipe Issues 

Dip pipes and H-pipes allow water effluent to move from one part of the tank to the next. If these pipes are clogged or broken at the top, water cannot move through as it should. This will result in issues, including that your tank might not drain. 

For example, if the H-pipe in the center is clogged, water will literally be trapped in the first area of the tank. This means your tank will fill up much more quickly, causing flooding. 

Here, the issue is relatively easy to fix. In most cases, you can simply check the H- and Dip pipes from the top. In others, you’ll have to dig them out to do so. 

7. Hydrostatic Pressure Problems 

If the ground around your septic tank is waterlogged, you can make the problem worse by attempting to pump it out.

Here, your septic tank will become buoyant because of hydrostatic pressure from the ground. This could cause it to lift, even slightly on one end. Then, it could begin to have drainage issues. 

If you’ve done this and are now having drainage issues, the only fix is to remove the septic tank and reinstall it.

That will mean digging up the area, re-excavating the ground underneath, and then reburying the tank. You might also have to replace any damaged parts. 

8. Overuse 

Most septic tanks are sized to the expected water demand and usage of the household. But, if that usage suddenly escalates, you might see sudden drainage issues.

For example, if you have the whole family over for Christmas and suddenly your drainage tank is full. It likely means the drain field isn’t designed to drain quickly enough to meet the new water demands. 

If the issue is temporary, you can simply wait it out. However, if you expect increased water usage to be an ongoing thing, the only fix is to replace the drain field or the tank itself. 

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Septic Tank Maintenance Tips

Photo: Virginia Sea Grant / Flickr / CC BY ND 2.0

Regular maintenance can keep your septic tank in good shape, so you never have to deal with flooding.

These maintenance tips will help you get started. 

Keep Plants Off The Drainage Field 

It’s okay to have grass and other shallow-root plants on the drainage field. However, any other plants can cause issues. That’s because roots will grow into the open holes in the drainage pipes.

That’s also true with trees. You should always have root barriers and harder and compacted dirt installed around your septic tank as a barrier. 

Empty The Tank On Schedule 

Most septic tanks should be pumped out every 3-5 years. The frequency depends on the size of the tank and the volume of use.

However, pumping too often can cause hydrostatic issues and the tank itself lifting. It’s especially important not to pump it out when the ground is wet. 

Keep Gutters Clean 

If gutters clog or flood water onto the drainage field, it can cause your septic tank to flood. Here, you want to make sure gutters don’t become clogged.

In addition, you should ensure that gutters drain in the opposite direction of your drain field. 

Don’t Drive Over The Septic Area 

It’s important that you don’t compact the dirt over your septic tank or the drain field. Here, most people use stakes or markers to ensure that they don’t. It may also be a bad idea to use a heavy riding mower over the area. 

Compacted dirt will be prone to flooding. In addition, it could damage the pipes underneath. And, if it’s over the drainage field, the dirt could also clog the holes. 

Don’t Flush Food Waste 

Food waste can cause problems by building up or by failing to decompose.

In addition, if your food waste is full of fat, it will cause fat lumps and buildup. This can cause major issues for your septic tank over time. 

Don’t Use Harsh Cleaning Chemicals 

Harsh cleaning chemicals are okay to use on occasion. However, if you’re bleaching your sinks and toilets every few weeks, you will disrupt the bacteria in your septic tank.

Eventually, that will mean that your septic tank stops decomposing properly. 

Occasionally Have Your Septic System Checked 

If you start noticing issues with your septic tank, you can always have the bacteria levels checked.

Here, a professional will help out, measure the levels, and then reinfuse bacteria where needed. This ensures the ecosystem in your septic tank stays balanced. 

To End

If your septic tank is full of water and not draining, the issue is likely a clog, drainage field issues, or dirt compaction. You’ll have to inspect the tank and where the water is overflowing to decide. However, it’s important that you wait to pump the tank empty until you’ve found the issue. Good luck getting your septic system back up and running