A Good Time to Review Tank Maintenance Procedures

Jim Anderson
Jim Anderson

A neighbor recently asked me that age-old question: “How frequently should septic tanks be cleaned?” This query popped up because our county requires an assessment of a tank every three years to determine whether the tank should be pumped. How often the tank needs to be emptied depends on a number of factors, including tank capacity, number of people using the system, whether there is a garbage disposal and how water is used in the house.

Before we go further, one note on the common words used to indicate the tank needs to be pumped. Like my neighbor, many laymen use the word “clean” when describing septic service, which could lead to misunderstandings. Saying a tank will be cleaned may indicate to some that the tank will be scrubbed, chemically treated or disinfected. Obviously we in the wastewater industry know that’s not what’s happening when you pull up with the vacuum service truck. So for the purposes of consumer education, let’s stick to “emptying” or “pumping” the tank.

Three years is considered an average threshold for the accumulation of sludge and floating scum in the tank to reach the point where they occupy 25% of tank volume. This is a somewhat lower volume than the 33% level that was recommended in the 1970s and ’80s. The bottom line is to prevent solids from being discharged to the soil treatment unit. Periodic tank pumping, along with installation of effluent screens, can dramatically reduce solids impacts on soil treatment areas.

Periodically evaluating septic tanks can have some other benefits. Baffles can be inspected to make sure they are in place and operating. Tank operating level can be checked to determine if there are any leakages or backups. Effluent screens can be cleaned and accumulation of solids measured, allowing an estimate of the rate of solids buildup.


Personally, I have my tank pumped every three years. This allows my service provider to get a good look at the inside of the tank to inspect for any excessive corrosion and the occurrence of cracks and potential leaks. To me, this is a good “insurance policy” to make sure I protect my soil treatment unit. Replacing the soil treatment part of the system is usually very expensive!

The next question on the part of homeowners is: What should be done to empty the tank properly? As a service provider, part of your responsibility to the homeowner is to explain what you need to do to properly pump and evaluate the tank. I have addressed this question before, but it never hurts to revisit the issue because it is a question I get very often.

First, the tank needs to be opened. A proper assessment and pumping cannot be done through an inspection port! This means the maintenance hole needs to be located and opened. In what I like to call the “old days,” this required spending some time locating the tank — sometimes not a small task — and then estimating the location of the maintenance hole and digging down until you found it. Now most codes require the addition of manhole risers at or near the surface, making locating easier for the service provider.

If you have a customer where the depth to the opening is more than a foot, it’s a good idea to sell them on the benefits of adding a riser in time and money savings during future visits. That is in areas where raising the access is not mandated.

After the tank is opened and before any pumping occurs, the contents of the tank should be inspected. There should be three distinct layers: sludge on the bottom, a clear zone and the floating scum layer. If these layers are not present, it is a good indicator of some potential problems due to homeowner use or the presence of some water-using devices affecting tank operation.


A missing scum layer may indicate the pH of the tank is higher or lower than the optimum range for bacterial action or the presence of water softener recharge water. The clear zone should be 75% of the tank volume. If the zone is very cloudy and flocculent is present, it indicates a high BOD content as a result of large additions of alcohol or dairy. Total lack of a clear zone means there is some antibacterial use impacting proper bacterial function in the tank. A dark sludge may indicate the presence of an iron filter. Presence of any of these conditions calls for a discussion with the homeowner about their system use and the need for an increased maintenance frequency.

Proper tank evacuation means all solids and liquid are removed. The industry standard is that everything is removed to a depth of 1 inch. To accomplish this, the tank contents must be broken up and mixed. This can be accomplished either by mechanical mixing (my preference) or continual backflushing until the scum layer is broken up enough to be pumped into the truck.

When the tank is empty, it should be inspected to make sure the baffles are in place and are in good shape — not corroded. The tank should be checked for signs of cracks and leaks; just as important is to observe if water coming in from either the inlet or the outlet. If water is coming from the inlet and you had the homeowner refrain from using water while working on the tank, they have a leaky fixture that needs to be fixed. If water is coming from the outlet it may mean the drainfield is backing up into the tank and should be evaluated.

When the pumping is complete, the job of the service provider is not done until the cover on the maintenance hole and/or risers are securely placed to prevent unauthorized access. Most state codes address how these covers are to be secured. Know those rules and follow them. Every year, lack of secure covers results in homeowners or children falling into tanks, which can be fatal.

Finally, fix any damage to the lawn by replacing soil and sod that was dug up to locate the maintenance cover. Check to make sure you have not left anything behind in the way of tools and the site is cleaned.


Comments on this site are submitted by users and are not endorsed by nor do they reflect the views or opinions of COLE Publishing, Inc. Comments are moderated before being posted.