Written by: Dawn Nall, Research Engineer, Southwest Environmental Finance Center

If you own a home or other structure with a septic tank, you should be aware of the signs of a full septic tank.  You should also understand the stages of a full tank: Tank Filled to Normal Level, Sludge Accumulating, and an Over-filled Tank.  What do these three terms mean?   

  • Filled to the Normal Level is just as it sounds, the water can flow normally, as it should, and there are no problems.   
  • Sludge Accumulating is a normal part of the septic tank operation.  The solids enter the tank and build up inside the tank while the liquids pass through.  Once the solids occupy 1/3 or more of the tank, the tank should be pumped out.  
  • An Over-filled Tank has accumulated too many solids and can cause back-ups into the home or structure or may clog the drain field due to solids passing through to the drain.  Either way, the problems caused here can lead to costly repairs.   

If you have regularly scheduled tank inspections and pumping, you should not have to worry about the tank getting over-filled.  Regular maintenance is the key to success.  How often you need to pump your tank depends on the size of your household (or how much water you use) and the size of your tank. Knowing the signs of a full tank can be helpful.  So, what are the signs your tank is full? 


Image courtesy of Pat Moin via Unsplash

Signs your septic tank is full:


  • Pooling of Standing Water 

Be aware of any water standing or pooling around your septic tank.  This is a good sign that your tank has begun to overflow.  You may also notice pooling around the drain field.  This is caused by clogged pipes forcing the water to surface.   

  • Slow Drains or Flushing  

If you notice that multiple (or all) of the drains in your home have slowed down, it’s possible your septic tank is full.  The drains can slow when the tank is full, and the water can’t move as it should.  The same can be said if you notice the toilets aren’t flushing easily.   

  • Unpleasant Smells 

If your tank is operating normally, you should not smell anything coming from it or from your drain field.  If you notice any foul smells near your tank, drain field or in your household drains, this is a sign the tank is full.   

  • An Extra Lush Lawn 

It is normal for the grass above the drainage field to be a bit greener or nicer than the rest of the lawn, but an overly lush or super green lawn could mean you have a full septic tank.  

  • Sounds of Gurgling Water 

If you hear gurgling or bubbling sounds in your pipes, especially if the sound is regular, this is another sign your tank may be full.   

  • Sewage Backup 

The most obvious sign of a full tank is when raw sewage is backing up into your pipes.  This can also be the most costly sign.   

  • Well Water Impacts 

If your septic tank has been leaking into your yard, it could contaminate your drinking water well.  You will see high nitrate in your water tests if this has happened.   


Regular inspections are key

EPA recommends that you have your tank inspected and pumped every 3 to 5 years unless you have a small family size and/or a large tank size.  If you suspect your tank is full, you should call a septic service provider in your area.  You can search for providers at this site:  https://www.nowra.org/septic-locator/  

For more information on septic tank use, costs and maintenance see our resources at: https://infohub.swefc.unm.edu/odww/