Best Septic Tank TipsA Guide to Septic Cleaning – How Often Do You Pump Out A Septic Tank? (SEPTIC TANK PUMPING SCHEDULE)

Table I: given below lists the recommended septic tank pumping frequency according to septic tank capacity and household size. The frequencies were calculated to provide a minimum of 24 hours of wastewater retention assuming 50 percent digestion of the retained solids.

Common septic tank pumping frequency mistakes

  1. Failure to pump the septic tank frequently enough: leading to an early drainfield failure and costly repairs
  2. Pumping or cleaning the septic tank too frequently, wasting money (though you’re wasting a lot less money than the cost of a new drainfield.Some septic pumping contractors and some other “experts” give a fixed rule of thumb that serves their own interest, such as “pump your septic tank every year” or “pump your septic tank every two years” or in a case we know about in Minnesota, “pump the septic tank every couple of months or after you’ve had a lot of visitors”.It would be smarter to pump the septic tank before or both before and after heavy use if we know the septic system is marginal. Pump the tank before a period of heavy usage to avoid a sewage backup during the heavy usage interval and afterwards to get back to normal usage levels.See SEPTIC BACKUP PREVENTION for tips to avoid a septic problem during times of anticipated heavy septic system usage.

    Contractors may give this advice without first having actually considered any information about the septic system capacity, level of usage, age, or other conditions. It’s a great example of “OPM” or “other people’s money” – spending someone else’s money to reduce your risk that they’ll complain that your advice wasn’t safe enough.

  3. Pumping the septic tank with the fantasy that doing so will “fix” a clogged or failed drainfield. All you really gain is a few days of toilet flushing before the tank has re-filled.

See this complete list SEPTIC TANK PUMPING MISTAKES and fantasies about how septic tanks work and how they should be maintained.

Actually inspecting the septic system, diagnosing any problems or failures, and inspecting conditions inside the septic tank will tell us whether the tank is being pumped at the correct frequency.

The removal of septic waste by cleaning the septic tank is a critical step in septic system care as it extends the life of the septic field. Even if you don’t care how septic systems work you need to know when to clean the septic tank by pumping out septic waste. Using the septic tank cleaning frequency table just below, simply look up your tank size and number of building occupants to see how often the septic tank should be cleaned. Later in this article we list other factors that can increase or decrease the recommended pumping rate.

Table I. Septic Tank Pumping Frequency in Years

Household size – Number of Occupants
1 2 3 4 5 6 7 8 9 10
Septic Tank Size

Septic Tank Pumping Frequency in Years

500* 5.8 2.6 1.5 1.0 0.7 0.4 0.3 0.2 0.1
750* 9.1 4.2 2.6 1.8 1.3 1.0 0.7 0.6 0.4 0.3
900 11.0 5.2 3.3 2.3 1.7 1.3 1.0 0.8 0.7 0.5
1000 12.4 5.9 3.7 2.6 2.0 1.5 1.2 1.0 0.8 0.7
1250 15.6 7.5 4.8 3.4 2.6 2.0 1.7 1.4 1.2 1.0
1500 18.9 9.1 5.9 4.2 3.3 2.6 2.1 1.8 1.5 1.3
1750 22.1 10.7 6.9 5.0 3.9 3.1 2.6 2.2 1.9 1.6
2000 25.4 12.4 8.0 5.9 4.5 3.7 3.1 2.6 2.2 2.0
2250 28.6 14.0 9.1 6.7 5.2 4.2 3.5 3.0 2.6 2.3
2500 30.9 15.6 10.2 7.5 5.9 4.8 4.0 3.5 3.0 2.6

NOTES to the Septic Tank Pumping Schedule Table:

  • Numbers in the septic pumping table indicate septic treatment tank pump out in frequency of every nn years for conventional septic tanks, and assuming for year-round occupancy of the residence. (This data does not pertain to simple holding tanks which retain all solid and liquid waste with no treatment no effluent disposal system.)
  • * These septic tank sizes are below the minimum size allowed in Pennsylvania and other jurisdictions. Florida septic tank pumping rules and Ohio septic tank cleaning rules may be more demanding.
  • Minimum septic tank sizes: Under current Pennsylvania law a 900 gallon septic tank is the minimum size that must be used for a home with three bedrooms or less. If six people reside in a three-bedroom house, the tank should be pumped every 1.3 years. If the same system serves a family of two, the tank would be ready for pumping every 5.2 years. Systems installed before the current rules and regulations were implemented may need to be pumped more often, perhaps every year or less.
  • Garbage disposers will increase the frequency of pumping. For example, if this same three bedroom house with six residents had a garbage disposal and was generally producing a higher volume of wastewater, the pumping frequency would be calculated as follows: 1.3 years – [(0.2) x 1.3 years] = 1.0 year. For more analysis of the effect of garbage disposers on septic systems
    see Garbage Grinders or Garbage Disposes and Septic Tank Maintenance
  • Typical Septic Tank Pumping Costs: A typical fee to pump a septic tank is $200. to $300 to pump a septic tank up to 1000g in size, provided that the tank pumping access port has been uncovered and is readily accessible.If the septic pumping contractor needs to find the septic tank and then excavate the septic tank pumping access opening, expect to pay an additional $350. to $400. provided that no extraordinary measures are needed. Prices vary somewhat by region. A part of the fee you’re paying your septic pumping contractor is the cost to dispose of the septage.
  • For an explanation of the meaning of sewage levels in the septic tank and how that information informs septic tank pumping frequency,

Onsite sewage disposal system holding tanks, where there is no septic field, will need to be pumped more frequently based simply on the rate and volume of septic waste inflow. Portions of this information were provided by the Penn State College of Agriculture – Cooperative Extension.

We have edited and added to the original septic tank pumping guideline material based on research and field experience testing, inspecting, and installing septic systems and based on study of other reference sources on septic system maintenance and design.

Electronic Monitors for Septic Tank Scum & Sludge Levels Give Septic Tank Cleanout Frequency

Septic tank monitor

Below at References we also describe an electronic septic tank monitor or grease trap monitor from Worldstone.

These devices can track sludge, scum, or grease levels in order to best schedule septic tank pumping or grease trap cleaning. This product is suitable for commercial installations and possibly for some residential septic tank systems.

According to the company, “Data from monitors can help establish appropriate service intervals, and document maintenance for regulatory compliance. Alarm features can help detect abnormal conditions and prevent costly backups.“The company also produces an oil tank level monitor.

OPINION – DF: this product is a great idea for commercial installations or problem septic installations. Substituting actual septic tank scum layer thickness or scum level thickness data for the septic tank pumping schedule table above may allow the tank to be opened and pumped less often – saving some money.

Watch out: But don’t forget that regular opening and inspection of the septic tank, such as happens when the septic tank is to be pumped out or “cleaned”, gives an additional opportunity to check for other septic system problems that could be leading to a costly failure, but that don’t directly concern the septic tank sludge or scum layer thickness. Examples include the discovery of lost or damaged septic tank baffles, septic tanks leaks that allow ground water to flood the septic system, or septic tank leaks out of the tank.

Alternative Septic Tank Pumping Frequency Guidelines: the University of Minnesota Septic Tank Inspection Frequency Point System

The University of Minnesota has published “Septic Tank Pumping Frequency Guidelines” that take a different approach than the cookbook table of septic tank sizes and number of building occupants shown in our table above.

But the document does not really tell the homeowner when to pump the septic tank. Instead it calls for essentially very frequent septic tank “inspections” to decide if pumping is needed, without, regrettably, explaining what that inspection would entail nor how that inspection would decide that the septic tank needs to be cleaned.

Watch out: In sum, we cannot recommend this chart’s use as the best or sole option for deciding when to pump out a septic tank, nor does the chart actually answer that question, as we explain below.

However it would indeed be a “safe” approach to inspect the septic tank conditions at every one, two, or three years, which is the actual end result of this misnamed worksheet.

Septic Tank Pumping Frequency vs Septic Inspection Frequency – clarified

Instead of taking the widely-used septic tank size and number of bedrooms table approach, U.Minn. experts have provided a table or questionnaire that when answered, gives a septic tank inspection frequency in years. The appeal of this approach is that it allows a homeowner to take into consideration factors that would either increase or decrease the interval for septic tank inspection based on factors that increase or decrease the septic failure risks posed by the home and its usage. Unfortunately factors enumerated in the point-counting approach have some troubles of their own, as we explain below.

The added cost of annual to tri annual septic tank inspections might be weighed against the safety, fine-tuning, and “actual septic tank data” approach to septic tank inspection frequency we describe below, or the simple and easy to use septic tank pumping frequency table we provided above.

Watch out: the septic tank worksheet does list some interesting septic tank risk factors, as we elaborate below. However, overall the worksheet we reviewed underweights the septic tank failure risk of some factors and overweights or confuses others, and it does not directly address the risk of drainfield damage caused by flushing high volumes of wastewater (laundry, water softener) through the septic tank.

But the chart doesn’t do that anyway. Although the chart’s title is “Septic Tank Pumping Frequency Guidelines” it does not provide that information. Instead, if you complete all of the work and analysis in this chart, you end up at one of three frequencies at which you should inspect the septic tank condition to determine if it needs to be cleaned:

Septic System Failure Risk Level Factors
Septic Worksheet Risk “score”
0-8 = Low Risk 2-3 year septic tank inspections: Evaluate the septic tank conditions every 2-3 years to see if cleaning is needed. In MN some municipalities require septic pumping or inspection every 3 years. Requirements vary in other U.S. States & Canadian Provinces as well as of course municipalities in other countries.
8 – 18 = Medium Risk 1.5 – 2.5 year septic tank inspections: Evaluate the septic tank conditions every 1 1/2 – 2 1/2 years to see if cleaning is needed
19-26 = High Risk Annual septic tank inspections: Evaluate the septic tank every year to see if cleaning is needed
Adapted from the U. Minnesota septic tank pumping frequency worksheet cited below at reference [5][5] “University of Minnesota Septic Tank Pumping Frequency Guidelines”, University of Minnesota, 2009 for extra copies of the original chart call (800) 322-8642, retrieved 1/15/2010, original source:
@ostp/documents/asset/cfans_asset_126408.pdf [copy on file as U_Minn_Septic_Pumping_Chart.pdf]

U.Minn assigns a numeric value such as 0, 1, or 2 or for some items 0-4 as the septic system load is likely to be increased. The homeowner adds up various risk number totals to reach a “risk score” that puts their system into one of three categories of septic tank “evaluation” frequency. “Evaluation of the septic tank ” here means determine if it needs to be cleaned.

Evaluate the Septic Tank ?

Really? What the heck does “Evaluate the Septic Tank” mean? This question is not addressed in the UM worksheet. Without septic tank inspection points, pass/fail criteria, or trouble signs for which the “evaluator” is to be alert, we just don’t know what to make of this advice and we certainly can’t expect any consistency in the results.

However we answer this question in excruciating detail beginning at SEPTIC TANK INSPECTION PROCEDURE where we list many things that should be evaluated to avoid septic system failures or worse, unsafe conditions; or you can “cut to the chase” as mom says, and have your septic contractor open the septic tank and MEASURE SCUM & SLUDGE, to know objectively if the tank needs pumping.

Watch out: “Evaluation of septic tank condition” is not well defined. Experts generally agree that there are a number of inspection points including the septic tank sludge and scum layer thickness that determine that septic tank pumping is needed (or not) but that there are other inspection points that are very important such as evidence of backup, damaged baffles, tank flooding or septic tank leaks, and of course septic tank safety: safe covers, no signs of collapse risk, etc.

Some Factors that Should Increase the Septic Tank Pumping Frequency

  • Use of a garbage disposer or food waste grinder increases septic tank pumpout frequency – we agree, but not all experts do. See GARBAGE DISPOSAL vs SEPTICS for details.
  • Use of a sewage ejector pump connected to the septic system may increase septic tank pumpout frequency by adding macerated sewage that increases the risk of pushing floating solids into the drainfield. See SEWAGE EJECTOR / GRINDER PUMPS
  • Use of a water softener or water conditioner such as an iron filter whose regeneration cycle water empties into the septic tank may increase the tank pumping frequency, though this is arguable in our opinion. Issues are excessive salt dosage that is going to reduce septic tank bacterial action but worse may seriously damage a drainfield; also the water volume itself can flood a marginal drainfield.See REDUCE IMPACT of SOFTENER on SEPTIC and also our discussion of the effectsof SALT OR WATER INTO SEPTIC
  • Frequency of use of laundry facilities; similar questions and arguable facts as with water conditioners. However installing a septic filter to keep fabric filters out of a septic tank or drywell can give significant benefit as can avoiding excessive volumes of powdered detergents. And as with water conditioners, the effect of water volume on the drainfield may be more immediate and serious than the effects of laundry water on the septic tank.
  • The U.Minn. table adjusts the laundry impact on septic tanks and septic tank risk levels downwards if you
    • use a water-conserving top loading washer or a front-loading washing machine [presumably they mean that either unit should be water-conserving]
    • have installed low flow shower heads
    • have installed low water usage toilets
    • repair [water supply system] leaks [such as drippy faucets and running toilets] quickly
    • use mild cleaning products & detergents and limit use of anti-bacterial products – in our opinion arguable as the level of antibacterial effect of at least some popular brand dish soaps has been estimated as trivial; I would have instead increased the risk level for constant or frequent use of antibiotics by occupants of the building, as nursing homes, for example suffer septic tank bacterial action reduction from that cause
  • An in-home business that increases water usage (daycare, taxidermy, hair salon) increases septic tank damage risk – same arguments as we suggested above should lead one to be concerned about the drainfield when added waste water volume rather than added solids are present; some home businesses (photography or taxidermy) include use of chemicals that should not be flushed into a septic system.See TOILETS, DON’T FLUSH LIST.
  • Having 3 or more overnight guests at a time or large groups visiting the home add septic tank risk; the table and approach does a poor job of distinguishing between 3 overnight guests once a year and regular extra sleepover guests; similarly, occupancies that place more than the usually-assumed 2 occupants per bedroom should cause a septic tank pumpout frequency increase
  • Septic tank size vs number of bedrooms: here we are in full agreement about the impact of high number of bedrooms and small septic tank sizes, but adding risk points for “don’t know” is a bit vague.
  • Time since last time the septic tank was cleaned affects the risk level – we agree completely. The worksheet adds one risk point if it’s been 3-5 years since last septic tank cleanout and 2 risk points if it’s been more than 5 years. In our OPINION this is a ridiculously weak weight placed on this critical factor.We regularly hear from people who have lived in a home for fifteen or twenty years and don’t recall ever pumping out their septic tank, nor where the tank is located, nor what size it is. Those are likely to be much higher risk situations than a 1500-gallon tank at a home with two people that was last pumped out six years ago.

Thanks to Inspectapedia for this great article