Guide to septic tank baffles & tees:
This document describes how to inspect the condition of septic tank baffles at the septic tank inlet baffle and septic tank outlet baffle ports.
Septic tank baffles are a key component of septic tanks which prevent damage to the drainfield by reducing effluent agitation as sewage enters the septic tank, and by preventing solids from flowing out of the tank to the drainfield.
If the septic tank baffles are damaged, missing, or were never provided in the first place, the life of the drain field or leach field will be seriously shortened. Inspecting concrete septic tanks is a key component in onsite wastewater disposal systems.
Green links show where you are. © Copyright 2015 InspectApedia.com, All Rights Reserved.
In the sketch at left the inlet and outlet septic tank baffles or "tees" are shown in brown and light blue respectively. You can see that the inlet tank baffle or tee will direct incoming wastewater down into the tank (not zooming across a tank to rush to the outlet opening).
Forcing the incoming sewage to make a right turn (down) also slows its impetus. This turn and downwards direction are even more critical in a one-compartment septic tank.
Image adapted from Alaska DEC  The dashed lines illustrate the liquid level (red) and the difference in elevation (green) between the inlet and outlet septic tank pipe connections.
You can see that both of these septic tank baffles or tank tees keep the floating scum and grease from blocking the septic tank inlet (at left) and importantly, the tee or baffle keeps the floating scum and grease from exiting the septic tank outlet (where it would clog the drainfield). If these components have been lost or damaged in your septic tank they need to be replaced or repaired, as we explain here.
If at the septic tank outlet the baffles are damaged or missing, or if no replacement "tee" has been installed, you can be sure that sewage has been pushed into the drainfield or absorption system, reducing its future life by speeding soil clogging there.
If septic tank baffles are lost or damaged (rusted off on a steel tank or broken off on a concrete tank), they can be repaired or replaced. For example at a steel tank the contractor may simply insert a plastic piping "Tee" into the tank inlet or outlet to create a new baffle system.
Baffles in a septic tank are provided to keep solids and floating scum and grease inside the tank. Baffles are provided at both the inlet to the tank (from the building) and the outlet from the tank (to the absorption system). The steel septic tank shown above at left has a baffle that is rusted away at its top.
On pumping this old steel septic tank one expects to see the baffle bottom has rusted off too. The home made septic tank shown above at right had no inlet baffle and a broken outlet baffle, factors in the rapid destruction of the leach field for this septic system.
Broken septic tank baffles or high sludge levels can cause solids to flow out of the tank and into the absorption system. The result is reduced absorption into surrounding soil and eventual failure of the system. Floating scum thickness and settled solids thickness can be measured through access ports into the tank or cesspool.
Our photo (left) shows an old steel septic tank with the baffle at the right side of the photo. Just touching the baffle with a tool showed us that it was rusted and collapsing.
This septic tank was pumped out, filled-in, and abandoned. But had the owners intended to use it they'd have needed to excavate the tank to install a baffle. That procedure is described in detail at SEPTIC TANK TEES.
Finding solids at or covering the outlets or damaged baffles should result in report of a very questionable adsorption system and possible major repair cost.
Depending on how long the tank was used without good baffles, the volume of solids and grease that moved from the tank to the absorption system will have begun clogging soils there and will have reduced the future life expectancy of the absorption system.
Baffle damage and repair, or even a complete tank replacement when the absorption system has been left alone always lead the author to warn the building owner that the future life of the absorption system may be in doubt and that additional expense will be involved.
As we mentioned above, see SEPTIC TANK TEES for instructions on how to install septic tank tees when septic tank baffles are damaged or missing.
Inspect for Damaged Septic Tank Baffles at Inlet & Outlet:
The condition of the septic tank baffles tells you what has been happening in the septic system.
Our photo at left, compliments of architect Jerry Waters, shows a badly deteriorated concrete septic tank baffle. Details of the septic tank baffle repair, involving installing a PVC tee in this septic tank, are shown at SEPTIC TANK TEES.
Concrete septic tank baffles may erode from chemicals, detergents, poor concrete mix, water flowing over top of baffles, or may be broken by improper pumping procedures.
Look for evidence that the floating scum layer is over or has ever been over the tank baffles - an indication of system failure that needs further investigation.
Inspecting for Septic Tank Baffle Overflow
When a septic tank is opened for tank pumping at a center cleanout port the baffles are not easily visible except indirectly by mirror or camera held inside the tank. However for this case we opened and inspected the septic tank inlet baffles.
This photo shows inlet sewer line (green pipe at left) and concrete baffle (at right) at the inlet end of a 1000 gallon concrete septic tank which is in use.
While the sewage level looks normal in the tank at the time of this photo, the sewage atop the concrete tank baffle suggested that the septic tank had been flooded in the past. We were concerned by the evidence that sewage had been flowing over the top of the baffle - an abnormal condition that could suggest a prior blockage either at the tank inlet baffle or at the tank outlet.
We decided to pump the tank, clean it, and inspect it further. The step by step septic tank opening, pumping, and inspection procedure are documented at SEPTIC TANK PUMPING PROCEDURE.
Ground water or surface runoff leaking into a septic tank will flood the tank and add to saturation of and early failure of the septic system leach field or drainfield. At the septic tank shown in these photographs, water was leaking into the septic tank around the tank inlet sewer pipe.
We located and corrected the probable source of water leaking into the tank. In this case the leak was at the inlet pipe to the septic tank where water was collecting by running down the hill into the sewer line trench.
The combination of a downhill trench headed towards the septic tank (the trench collects and aims surface and subsurface runoff water towards the septic tank), and a leak at the entry of the sewer pipe into the septic tank was causing the tank to flood.
We sealed the entry to the septic tank with concrete as shown in this photo of a concrete seal which we installed at the sewer line entry to the septic tank.
See SEPTIC TANK LEAKS - for an explanation of how and why septic tank leaks cause septic system failures.
At SEPTIC TANK BACK FLOODING we explain the causes of abnormally high sewage levels in septic tanks.
You cannot see the entire condition of the septic tank baffle before the tank is pumped, but inspect the baffle tops for evidence of corrosion, damage, total absence, or of sewage flowing over the baffle top (an indication of excessive in-tank sewage levels). Photos of the septic tank baffles in a concrete tank, as seen from inside the septic tank are provided at "Septic Tank Pumping Procedure" for which we provide a link at "More Reading" below.
The sewage level inside a septic tank should always be several inches below the baffle top but within a right at at or just below the bottom of the tank inlet pipe. If sewage level is low inside a septic tank which is in use, it is almost certain that the tank has been damaged and is leaking into surrounding soil.
Septic tank maximum scum and sludge buildup prior to pump out, and instructions for measuring the floating scum layer thickness and settled sludge layer thickness in a septic tank are available at SEPTIC TANK PUMPING SCHEDULE.
Also see MEASURE SCUM & SLUDGE for details of how we make these measurements.
See SEWAGE LEVELS in SEPTIC TANKS for details on normal and abnormal levels and what they mean. Our page top photo shows a typical concrete septic tank baffle at the inlet pipe. Steel septic tanks have a similar barrier installed.
If your septic tank baffles are damaged and need repair or replacement, see SEPTIC TANK TEES [live link given just below] for help on how to install septic tank tees when tank baffles are damaged or missing. It's an easy repair.
We also recommend septic tank outlet filters installed at the tank outlet tee to extend the drainfield life. [Live link given just below].
Continue reading at SEPTIC TANK TEES how to detect a lost or damaged septic tank baffle or a damaged tank tee; when & how to add a septic tank tee or select a topic from the More Reading links shown below.
Suggested citation for this web page
Green link shows where you are in this article series.
Frequently Asked Questions (FAQs)
Question: ok to chip a hole in the concrete tank to connect piping?
(May 23, 2014) Sophia Liam said:
Does chipping away at the concrete of the tank to put in the piping cause the tank to be more at risk for cracking in the future? This article was super interesting, so I'm just looking for a bit more information. You've got a great blog going here.
Sophia, septic tanks are normally cast with an opening for pipe connections. Chipping at the tank shouldn't increase the crack risk, but indeed any discontinuity in a concrete casting (e.g. windows in a foundation) can create a variation in stress that can be the locus of a future crack.
Question: elbow rather than tee at septic tank inlet
(June 7, 2014) Patrick said:
Also, the inlet seems to have corroded and severely narrowed the opening into the tank, likely causing the backups that lead to the pipe failure. Is there a way to "bore out" the cast iron inlet that is corroded, or do I need to look at replacing my inlet (and likely outlet) pipes? Can an expert knock out the old cast iron inlet and replace it with a new plastic one without damaging the tank?
I would excavate the tank inlet end, break out the corroded cast iron, and if there is no intact tank baffle inside the septic tank I'd cement a new plastic tank tee in place, sealing the tank opening around the tee with hydraulic cement or if the surfaces are clean and dry, a suitable flexible sealant.
IF the tank baffle is intact you can go straight into the tank in the baffle area with a new plastic line connection, just stop the projection in the tank flush with the tank wall.
Question: can I use an elbow instead of a tee
(June 16, 2014) brian said:
Brian I'm unclear on why you want to use an elbow instead of a Tee - which would make inspection and cleaning rather difficult and might increase the clog risk.
If you are thinking of inserting a Tee as an outlet or inlet baffle and wanted to extend that to the surface I'd prefer to install a septic tank riser of larger diameter, making inspection and cleaning much easier, but yes one could just extend a tee to the ground surface. Be sure to seal against leaks into the septic tank.
In the FAQs section of our sister article SEPTIC TANK TEES you'll see more about why installing elbows instead of tank tees is not a good solution for septic tanks. You may need to click to show and read those faqs.
Question: ok to build a floor over the septic tank?
(June 26, 2014) Don said:
Is it safe to put a concrete floor over a septic tank?
Is it safe to put a concrete floor over a septic tank? The flooring is around 4 inches, the only outlet pipe would be the one heading to the municipal sewage system.
Will there be methane problems?
With proper support the concrete floor may be "safe" but it's a design that makes for some big trouble in a year or two when the septic tank needs to be pumped.
You need to keep adequate access to inspect, repair, clean the septic tank.
Question: cost to install a septic tank baffle tee
(July 14, 2014) Mike Brantley said:
It might have been gouging, or it might have been quite fair. The parts are often the least costly part of a job. Other costs such as excavation and restoration work or pumpout if that was part of the job would of course increased the job cost.
Question: ok to move a septic tank inlet
(July 17, 2014) Keith said:
Most likley, yes, but you'll need to look into the septic tank to be sure that there is (or you'll need to add) an inlet baffle at the new inlet connection
Also, watch out: going from a mobile home to a new house, the size and capacity of the septic tank and drainfield may be inadequate.
Question: hubbie says don't need septic tank tees
(July 27, 2014) Amy said:
Amy you are completely correct.
Omission of the Tee or baffle at the septic tank outlet very seriously shortens the drainfield life by pushing solids out into the field piping.
Install an outlet tee or baffle.
The lines to the drainfield should not need "flushing" - if your husband thinks they do, it's because your septic system has been pushing solids into the piping.
If hubby still wants an opening to mess with the drainfield piping he should install a D-box outside of the septic tank between the solid line feeding the drainfield and the perforated drainfield piping network.
The details of your note make me worry about the correctness of the design and installation of your system.
Question: septic tank is full and overflowing - are the leach lines OK?
(July 29, 2014) Keith C said:
Keith if no effluent flows into the leach lines most likely the drainfield is saturated, flooded, or lines blocked. Try a test excavation at the end of one or more drainfield lines.
Question: pumping the septic tank every 6-9 months, exploring piping
(Sept 20, 2014) 9yr old house - continuous clogging of inlet piping said:
Right now there is no problem from the primary tank on. With increasing frequency, whenever we have a visitor, the system clogs. Responding, I use the snake from the primary tank toward the house and generally dislodge some visible amount of paper or otherwise release the clog and the system flows freely into the primary tank.
These days it takes someone visiting for just one night for the inlet to not work properly.
Inspect at the tank for condition of the baffles, for back flow into the tank from the drainfield, and then as needed check piping, perhaps by camera.
Question: OK to use a 90 degree elbow instead of a septic tank tee?
(Sept 25, 2014) Gene said:
I've seen 90's but a tee gives you the ability to see and clear clogs while the 90, pointing down, does not.
The tee also will allow sewage to overflow at the tee top and enter the septic tank if the tee outlet becomes clogged. A clogged 90 degree elbow outlet will give you a sewage backup in the building.
I'd stick with a Tee.
Question: septic pumper brok off the tank tee - do I need it fixed?
(Nov 23, 2014) Brandy Schultheis said:
He broke them off and was going to leave the tee pipe just floating in the septic tank itself but we had him get that back out of it. He then charged us for all the things he broke. I just need to know how important these are to the tank.
Absolutely - the broken tee should be replaced as soon as possible - lest you push solids into and destroy the drainfield.
And a broken pipe seal at a septic tank inlet or outlet risks admitting ground water into the tank, flooding it, or risks permitting septic effluent to leak out ant an improper location.
Question: can an air leak in piping cause a septic tank backup?
(Dec 6, 2014) Mike bevens said:
Generally if there is a leak in a septic line you'll more likely see effluent leaking out or sewer gas leaking out.
Question: I paved over the leachfield - soakbed - is that OK?
9 Jan 2015 Anonymous said:
. When I flushed the toilet and watch the water entering the septic tank it was coming out of the top of the "T" instead of the bottom. Is that normal?
There are only two of us living in the house full time a only a few times a years do we have company and heavy use on the tank. I did pave over my leach field and plant plants over another section of it. Did I compromise the leach field by doing so? I have friends two doors away that pump their tank about every fifteen years.
Your advice will be greatly appreciated. Thanks
Reply: paving over the drainfield is a serious error
Keep in mind that while pumping the septic tank on schedule can help preserve the life of the drainfield, once the fields are in failure, pumping doesn't fix anything
Waste coming out of the top of a tee suggests that either the tee bottom was blocked or the drainfield is saturated. Try clearing the tee bottom and checking the thickness of the floating scum and settled sludge layers.
You don't ruin a leach field with a small single event of sending it solids but yes, in general that's indeed a way to speed leachfield demise.
Tank pumping frequency is given and explained
Watch out: paving over a septic drainfield is likely to destroy it, first by damage during the driving of paving vehicles over the field and second because the pavement prevents part of the field's functioning that requires transpiration or evaporation of a portion of the septic effluent and third because the cutoff of oxygen from the soil will halt operation of and kill off the required septic digesting bacteria needed for proper effluent treatment.
Use the "Click to Show or Hide FAQs" link just above to see recently-posted questions, comments, replies, try the search box just below, or if you prefer, post a question or comment in the Comments box below and we will respond promptly.
Search the InspectApedia website
HTML Comment Box is loading comments...
Technical Reviewers & References