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SEPTIC SYSTEMS, HOME BUYERS GUIDE to
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SEWAGE EJECTOR / GRINDER PUMPS
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SINKHOLES, WARNING SIGNS
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TOILETS, INSPECT, INSTALL, REPAIR
TRAPS on PLUMBING FIXTURES
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WASHING MACHINES & SEPTIC SYSTEMS
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Septic tank cleaning or pumpout frequency guidelines or rules: this article provides a septic tank pumping schedule based on septic tank size and level of usage. This document explains a key point in how septic systems work: the septic tank & septic system cleaning schedule - when to pump out the septic tank.
We describe all of the reasonable methods for determining the recommended frequency for cleaning out a septic tank: using a cleanout frequency table, using objective measurements, using an electronic tank monitor. We also explain what is septic tank effluent retention time, why to measure septic tank scum and sludge levels in sum we provide a comprehensive guide to answering: How often should septic tanks be pumped?
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SEPTIC TANK PUMPING SCHEDULE - A Guide to Septic Cleaning - How Often Do You Pump Out A Septic Tank?
If you don't know where the septic tank is located, see SEPTIC TANK, HOW TO FIND.
At TANK INSPECTION PROCEDURE we describe how to inspect the septic tank before, during, and after tank cleaning operations. Septic system maintenance and repair are discussed in a collection of detailed articles listed at Septic Tank and Septic System Maintenance.
Also see SEPTIC TANK PUMPING PROCEDURE, our detailed step by step photo-illustrated guide to find, pump and clean a septic tank.
See Septic Backup Prevention for tips to avoid a septic problem during times of anticipated heavy septic system usage.
Table I 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.
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. Look up your tank size and number of building occupants to see how often the septic tank should be cleaned.
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.
Septic Tank Pumping Frequency Guideline, based on Objective Data Not Guessing
Because we wanted to give an objective, measurement-data based alternative to simple use of the septic tank cleanout frequency table above, here we explain how to use the actual scum and sludge thickness to decide that a septic tank needs to be cleaned more often or less often. Complete details of this approach are found at MEASURE SCUM & SLUDGE.
The table of septic tank sizes and number of household occupants as a good rule of thumb guide to how often a septic tank should be cleaned out well for most people.
For a better understanding of the condition of the septic system, when the septic tank is pumped, it should also be inspected by the pumper - in a series of steps
The answers to those more detailed septic tank condition inspection questions (and more listed at SEPTIC TANK INSPECTION PROCEDURE) give important information about the condition of the septic tank as well as the drainfield or soakaway bed, and can suggest repairs that can extend the life and safety of the system.
For the most objective approach to a very accurate septic tank pumping or cleanout frequency guide do this:
Either immediately if your septic tank is past due for cleaning, or at the next scheduled septic tank cleanout otherwise, ask the septic contractor to actually measure the thickness of the settled sludge and floating scum layer in the septic tank. To understand just how these measurements are made, see our description of the whole process beginning at MEASURE SCUM & SLUDGE. That article series includes complete details such as:
Illustration courtesy Carson Dunlop Associates
At a Septic Tank Cleanout, Actual Septic Tank Measurements Will Tell You When Next to Pump the Septic Tank
The dashed "effluent" area shown in our septic tank illustration at left is also referred to as the "net free area" in the septic tank. When this area becomes too small the result is that wastewater entering the septic tank won't have enough settling time or septic effluent retention time for the solids to be broken down, sink into sludge, rise and coagulate into floating scum. If the septic tank net free area is too small and settling time too short, the result is that solid waste is pushed out into the drainfield - where it destroys the septic fields by clogging the soils there.
How to Interpret the Meaning of Septic Tank Sludge & Scum Layer Thicknesses in Deciding When to Next Pump the Tank
In simplest terms, if you open and pump a septic tank on the schedule recommended in the table above, then based on what sludge and scum layer thicknesses you find, you are going to pump the septic tank sooner next time, or you are going to be able to wait longer for the next cleanout, provided that other conditions such as number of building occupants or wastewater usage levels don't change.
Septic tank pumpout example - 3 occupants, 1250 gallon tank, pumped 5 years ago - cleanout interval can be extended
A household of three people is served by a 1250-gallon septic tank. The tank was last pumped five years ago. According to the septic tank cleaning schedule table above on this page, the tank should have been pumped after 4.8 years - so we are a little bit late. So we get our septic contractor over promptly and she opens the septic tank, inspects, pumps, cleans, and inspects again.
The septic contractor reports no evidence of failure, damage, problem with the tank. She also says that the tank had just about 3-inches thickness of settled sludge on the tank bottom - not much - and the floating scum layer was just 4-inches thick - very little in her opinion.
With this data, and if site or usage conditions don't change, you should be able to safely go another five years before the next pumpout, and could probably extend that to seven years (in my OPINION).
At the next (extended septic tank cleanout), check the sludge and scum thicknesses again. If they are still close to what you found in this cleanout, you're operating the septic tank safely.
Septic tank pumpout example - 3 occupants, 1250 gallon tank, pumped 5 years ago - cleanout interval needs to be shortened
A household of three people is served by a 1250-gallon septic tank. The tank was last pumped five years ago. According to the septic tank cleaning schedule table above on this page, the tank should have been pumped after 4.8 years - so we are a little bit late. So we get our septic contractor over promptly and she opens the septic tank, inspects, pumps, cleans, and inspects again. Just like the case above.
But this time the contractor says: Geez your septic tank was packed with sludge and scum - you had less than six inches between the bottom of the septic tank outlet baffle and the top of the settled sludge layer - your tank was "full".
In this case, and if site or usage conditions don't change, you need to start pumping the septic tank more often than every 4.8 years, - try 3.5 years or less next time.
As we elaborate at MEASURE SCUM & SLUDGE,
Similar rules of thumb offered by USDA on how much sludge or scum mean the septic tank needs cleaning include:
For a greater understanding of septic tank pumpout scheduling based on actual measurements, also see:
Electronic Monitors for Septic Tank Scum & Sludge Levels Give Septic Tank Cleanout Frequency
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.
Thanks to reader Robert Shirley for this tip.
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 mis-named 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:
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 ?
What does "Evaluate the Septic Tank" mean? This question is not addressed in the UM worksheet.
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 thicknesses 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
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Frequently Asked Questions (FAQs) about the pumping or cleanout schedule for septic tanks
Question: Recent Septic System Repair / Pumpout
I had some work done recently and if I sent a picture of the work, can you give me an idea of the quality of work? BTW, I love your site. - Syd
A competent onsite inspection by an expert usually finds additional clues that help accurately diagnose a problem. And certainly from a photograph alone one can't make a full nor accurate evaluation of the condition of a septic system.
That said, I'll be glad to look at your photos and if the initial Q&A is sufficiently modest I will reply pro-bono. Of course as you gave no information about the topic, I can't say in advance how much I can comment on the pictures.
Reader comment - followup:
I appreciate it. I used the information extensively when I bought this house. It is what clued me into the FPE panel I had and why when walking on the floor above the panel, the lights would sometimes dim (the breaker for the water heater was loose and arcing to the bus bar). I replaced the panel, breakers, etc..
Here are the specifics: Built in ‘84, in TN 4 BR, 2 bath, split foyer. Just my wife and I live here. Previous owners had 5 kids. The washing machine is on a proper grey water disposal system. The dish washer will be added soon.
Here's the story.
What started out 2 Friday's ago with a day off, I called the honey wagon to pump the tank. I have lived here for nearly 4 years and when I bought the house, the previous owners had the tank “inspected” and were informed that the tank did not need to be pumped. They lived here for 7 years and never had it pumped or checked. Now, the truck shows up and we start digging. Turns out that its not possible that the people that the previous owners had check the could have. The amount of dirt disturbed vs what I had to dig was way off. So the truck leaves and I dig a hole that is 5 feet deep by 4ft by 3 ft. By hand.
Fast forward to yesterday, truck comes back and we open the lid. This is when we find out that its approximately 2000 gal precast cement tank with 3ea 2.5x4ft hatches. Apparently this is rather uncommon around here. Also find that the exit baffle is nearly disintegrated however still in place. There was not an input baffle, in fact, it was a pipe that just poured waste onto the surface. The scum layer was 5 to 8 inches thick. I do not know how thick the sludge was, I had to go to home depot to get some pipe. Also, the input was right next to the output.
The driver pumped as much as he could (truck filled, he was expecting a 1000 gal tank which is common in this area), he got most the sludge and scum, 2/3 total volume removed. He recommended that a piece of pipe 2 ft. long be added to the input and to add a 4 in pipe with a tee on it. His method for installing the tee was to use PVC cement to a 2 ft long pipe, stuff the pipe down the output and secure with expanding polyurethane (great stuff) foam. You can see all of this in the picture. The pipe leaving to the drain field is orangeburg.
Here is what I think I know to be true: The tank was never correctly installed. I should have had the input moved and a tee or baffle installed. I should have asked him to come back to pump the rest of the liquid. I need to replace the orangeburg pipe soon.
So here are my questions: Since the system has been running like this 27 years and not pumped in at least 11 (could be 27 as well), do you think ill get another 10, maybe 20 out of it? Since the tank is rather oversized and its only the two of us, I think its safe to say the system is not taxed that much. We put a half gallon of spoiled buttermilk down the drain each month.
Thank you again for your assistance and for providing such an informative site with ACCURATE information. Feel free to use my picture of a hall of shame or whatnot.
Reply: Buttermilk is not a useful treatment to add to a septic tank
About your note and photo - just in order of thoughts & your note:
7+4=11 years, probably longer than recommended for pumping the septic tank - see http://www.inspectapedia.com/septic/Septic_Tank_Pumping_Schedule.htm
2000 gal precast cement tank with 3ea 2.5x4ft hatches - probably a good tank, certainly decent size; if the liquid/sewage levels were normal then the tank is not cracked, damaged, leaking.
It would have been better to pump the whole tank out completely - we don't know really if the sludge was adequately removed from tank bottom, though it's possible for the pumper to probe and measure the sludge thickness that remained.
It was absolutely correct to add the tee at the inlet - it reduces sewer gas and sewage backflow into the incoming sewer line; I'm not experienced with using expanding foam to secure the tee
if it works both to hold the tee in place AND there is no groundwater leaking INTO the tank at that end, you're in good shape.
YOU SHOULD open the OUTLET end of the tank and be sure that there is an outlet tee in place - this is critical to avoid sending solids into (and ruining) the drainfield
Orangeburg pipe: old, very old, questionable condition; I'd like to see any photos if you dig up any of that material.
If you find there was no outlet tee, combined with infrequent pumping and orangeburg pipe, you will want to be saving/planning for drainfield repair/replacement.
Inspect the septic drainfield area for wet spots, smells, evidence of failure.
I can't for sure predict how much life remains - a lot depends on level of usage, soil conditions. I've mentioned the tee - a predictor of field failure if it was missing.
Buttermilk is not a useful septic system treatment, though it won't hurt anything. You don't need to treat the system and in fact some treatments are harmful, even illegal. See http://www.inspectapedia.com/septic/Septic_Tank_Treatments.htm
Reader follow-up comment:
I think I may have been misleading. The input from the house is the 3 inch pipe towards the top of the picture (under the shovel). It originally was just a 3in 90 that poured onto the top of the surface. The outlet is the field is the 4in tee. The input is now under the scum layer and does not have a tee. My picture shows what should be the output, however, when installed it appears that the contractor put the input on that side as well.
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