What Is a Septic Tank Baffle?

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If you're experiencing backups in your septic system, accompanied by sewer smells in the house, and you can't seem to find a blockage in the drain pipes, the problem could be in the septic tank itself. The tank has a pair of baffles -- one at the inlet pipe and one at the outlet -- that prevent floating materials from flowing directly across the tank and into the drainage field. If the inlet baffle is worn or broken, effluent may back out of the tank and into the plumbing. By protecting the drain field from the floating layer of debris in the tank, the baffles perform a vital function in the septic system.


Septic Tank Design

A septic tank is a large water storage tank. Most hold from 1,000 to 1,500 gallons and are made from plastic or concrete. Sewage, which enters the tank through an inlet port and biodegrades inside the tank. Solids settle to the bottom and liquids flow through an outlet port to a drain field where they percolate into the ground and become naturally purified by the soil.


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The Purpose of the Baffles

The baffles are barriers placed in front of the inlet and outlet ports -- they may be built into the tank and made from the same material as the tank itself or they may be tees connected to the inlet and outlet pipes. Their purpose is to interrupt the flow of water carrying solids. The baffle in the inlet changes the flow direction 90 degrees and forces water down into the tank, while the baffle at the outlet port prevents the surface layer of water, which contains a scum of grease and decomposing sewage, from flowing into the outlet pipe.


Without the baffles, sewage would have a direct route from the inlet pipe to the drain field, which would defeat the purpose of the septic tank.

Symptoms of Ruptured Baffles

It isn't unusual for baffles on older septic tanks to develop holes or simply wear away. The definitive test to determine whether or not that has occurred is to open the tank and look, and a few operation symptoms can alert you to the need to do that:


  • Plumbing backups​ -- When the inlet baffle wears out, sewage might flow backwards from the tank into the house, or surface scum might prevent sewage from entering the tank. Backups can also result from clogs in the drain field caused by failure of the outlet baffle.
  • Sewage smells​ -- Whether in the house or in the drain field, sewage smells indicate that unprocessed sewage may be clogging the drain field, and that could be a result of baffle failure.
  • Soggy drain field​ -- If grease and scum are entering the drain field because of a failed baffle, it interferes with drainage, and you may notice standing water or unusually healthy vegetation in the drain field.


Inspecting the Baffles

If your tank has built-in baffles, it should have a manhole access over the inlet and outlet ports; you can determine the condition of the baffles by lifting the covers and making a visual inspection. Many tanks have inlet and outlet tees made from PVC pipe instead of built-in baffles. One port of the tee extends down into the tank and the other extends above ground and is capped. These pipes don't wear out, but they can get blocked. Remove the cap and look inside with a flashlight to make sure there are no obstructions.


If you discover problems with your septic baffles, call for help. Besides being highly unpleasant, working with septic tanks can be dangerous.


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