LARGER IMAGE: when you can see the SEPTIC TANK during installation or after finding it for a pumpout, that's a good time to measure off and record the exact location of the tank and its cleanout openingsSeptic Tank Inspection
How to Inspect Septic Tank Condition

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How to inspect the condition of a septic tank: this document describes in detail how to inspect the condition of a septic tank - a key component in onsite wastewater disposal systems.

We describe what to look for at three distinct septic tank inspection points: before pumping, during pumping, & after the septic tank has been emptied.

After discussing a list of things to watch for before, during, and after pumping or cleaning out a septic tank, we discuss specific septic system inspection details and concerns for steel septic tanks, concrete septic tanks, home made septic tanks, fiberglass or plastic septic tanks, and the condition of septic tank baffles.

We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

Inspecting Septic Tanks: How to Inspect the Condition of A Septic Tank

PHOTO of septic tank sludge being broken up for tank cleaning

The purpose of the treatment tank or "septic tank" is to contain solid waste and to permit the beginning of bacterial action to process sewage into a combination of clarified effluent, settled sludge, or floating scum in the tank.

An intact, un-damaged septic tank is normally always filled with these materials.

However the inspector performing a "visual" check of the septic system needs to be alert for some important findings which we describe below.

Here we will discuss the following:

Our photograph above shows a septic tank that has been opened with pumping in progress. You can see the septic pumping truck in the background. The septic pumping contractor is using a long handled tool to stir the septic tank scum and sludge to break up these deposits to ease their removal from the septic tank.

[Click to enlarge any image]

How to Inspect the Septic Tank Before & After Pumping

Photograph of a septic tank interior inspection tool using a pole, mirror, and flashlightIf you have not already reviewed SEPTIC TANK SAFETY please do so before continuing in this section. There are serious risks of injury, explosion, and death if safe procedures are not followed when working on septic systems.

Our photograph illustrates a simple but effective septic tank inspection tool: an extension pole that sports an adjustable mirror and a bright flashlight.

The septic tank mirror, set to an appropriate angle, combined with light from the flaslight, permits inspection of the interior of the septic tank after it has been emptied.

The septic pumping contractor may check the condition of the septic tank baffles, the cleanliness of the septic tank, and she will look for cracks, breaks, or damage that might explain a septic tank leak.

Septic Tank Safety Warnings

Watch out: Read these life-safety warnings before attempting to open, inspect, or do anything to a septic tank.

A Septic Tank Inspection Checklist

PHOTO of an unsafe septic tank cover placed over collpasing concrete blocksInspecting the Septic Tank and Septic Tank Area Before Opening the Septic Tank

The stacked concrete blocks were tumbling and the opening into the septic tank was larger than the cover.

We covered the area with plywood, roped it off, and informed the appropriate parties including the property owner.

A safe septic tank cover on a concrete tank is shown in a photo below where we discuss concrete septic tanks.

Probing in the area of a tank, without excavation, is not recommended as the probe may damage a steel or fiberglass tank.

Inspecting the Septic Tank After Opening the Septic Tank but Before Pumping

PHOTO of the septic tank muck raking tool used to break up scum
and sludge layers during pumping.When a septic tank has been located and uncovered for pumping, additional critical details may be observed before the pumping operation begins.

After Opening But Before Pumping the Septic Tank: When the septic tank is opened before it has been pumped out or cleaned, important information about the condition of the septic system is available:

See SEPTIC TANK LEAKS - for an explanation of how and why septic tank leaks cause septic system failures.

See SEPTIC TANK LEVELS of SEWAGE for an a discussion of: What Do the Levels of Sewage in the Septic Tank Mean about Septic Tank Condition, Septic Tank Leaks, & the Timing of Septic Tank Pumping.

Septic tank leaks are also discussed at SEPTIC FAILURE CRITERIA

Septic Tank Solids: floating scum & settled sludge thickness, net free area, effluent retention time

Solids entering a septic tank are intended to remain there until pumped out during tank service. A large portion of solids settle to the bottom of the tank as sludge.

Grease and floating scum remain at the top of the sewage in the tank. Baffles (discussed above) help keep solids, scum, and grease in the tank. Bacterial action in the tank make a modest reduction in the solids volume and begin the processing of sewage pathogens, a step later completed by soil bacteria in the absorption fields.

A separate document, MEASURE SCUM & SLUDGE, discusses how and why to measure septic tank scum and sludge

Net free area in the septic tank: If the sludge level becomes too high or the floating scum layer too thick, in addition to risking passage of solids out of the tank (damaging the absorption system), the remaining "net free area" of liquid in the tank is reduced. When the net free area becomes too small, there is insufficient time for waste entering the tank to settle out as bottom sludge or top floating scum.

The time allowed for sewage to separate and settle out as sludge or collect as floating scum is called septic tank retention time. Retention time is discussed further at EFFLUENT RETENTION TIME "Septic Effluent Retention time and Effective Septic Tank Volume - Why pump a septic tank before it is "full" of solids and grease?".

For an in-use septic tank with a small net free area, and therefore a short septic effluent retention time, the frequent entry of solid and liquid waste will keep the tank debris agitated, thus forcing floating debris into the absorption system where the life of that component will be reduced (due to soil clogging).

The importance of keeping an adequate net free area in a septic tank is the reason that tanks need to be pumped at regular intervals. Building owners who never pump a tank until it is clogged have already damaged the absorption system and reduced its future life expectancy.

Septic Tank Inspection During Tank Pumping

PHOTO of an septic tank during tank pumping.

During Septic Tank Pumping: if the pumper observes (or hears) septic effluent flowing back into the septic tank from the tank outlet pipe this is a sure indication that the drainfield or soil absorption system is waterlogged, and indicates a system failure needing further investigation.

The photo shows a concrete septic tank during pumping.

As the effluent level dropped below that of the bottom of the tank baffles, we stopped pumping briefly to listen for the sound of effluent flowing back into the tank from its outlet.

Septic tank pumping is best performed from an access cover at the center of the tank if one is provided (as in this photo).

This gives best access to the pumper to clean sludge and debris from all areas of the tank bottom.

Details about what to look for during the septic tank pumping operation are found at


Only by pumping and visual inspection can the septic tank capacity and condition be completely determined.

Septic Tank Inspection After the Septic Tank has Been Pumped Out

PHOTO of an septic tank when pumping out has been nearly completed.Details of what to look for when inspecting the septic tank's interior condition are at INSPECT the SEPTIC TANK AFTER PUMPING.

Here is some basic advice:

Watch out: Do not enter or lean down over or into any septic tank unless you're wearing special breathing apparatus and have a second worker watching you for safety - methane gas in the tank can cause fatal asphyxiation.

It should never be necessary to enter a septic tank. Any work to replace the baffles or repair the tank should be done from the outside.

After the septic tank has been pumped out it may be useful to inspect its interior for evidence of cracks, settlement, or damage to its baffles, or perhaps to confirm the tank size if most of the tank has remained buried.

If a septic tank has been serviced by removing a cover over the entire tank all of these conditions can be seen easily. But more often the tank is pumped by access through a center cleanout port.

If there is no center cleanout port on a septic tank (some older concrete tanks) it is pumped preferably at the outlet end of the tank but possibly at the inlet end.

Septic pumpers may use a combination of a mirror at the end of a pole and a flashlight to look at the tank interior to look for evidence of damage to the tank itself such as cracks, leaks, or additional evidence of damaged tank baffles.

At MEASURE SCUM & SLUDGE we include a detailed description of tools use to examine the condition of a septic tank before, during, and after pumping, including the pole, flashlight and mirror we show below.

Photograph of a septic tank interior inspection tool using a pole, mirror, and flashlight


Continue reading at SEPTIC TANK LEVELS of SEWAGE or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see SEPTIC TANK INSPECTION FAQs - questions & answers posted originally on this page.

Also see SEPTIC TANK LEVELS of SEWAGE for an a discussion of: What Do the Levels of Sewage in the Septic Tank Mean about Septic Tank Condition, Septic Tank Leaks, & the Timing of Septic Tank Pumping.

Detail about septic tank tees and baffles is at SEPTIC TANK BAFFLES.


Or see INSPECT the SEPTIC TANK AFTER PUMPING where we describe septic tank inspection mirrors, cameras & other tools

Or see these

Septic Tank Inspection Articles

Suggested citation for this web page

SEPTIC TANK INSPECTION PROCEDURE at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.


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Publisher - Daniel Friedman