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Septic tank cleanout timing based on objective data:
Determining septic tank cleanout frequency based on physical inspection of the septic tank scum & sludge layers. This article explains when to pump the septic tank and sludge and scum layer thicknesses.
We explain that making these basic observations when a septic tank is pumped, and knowing how long it has been since the previous pumpout can tell us more accurately when the septic tank is going to next need cleanout. This approach can save you money in pumping costs or it may save you money by properly protecting the life of the septic system drainfield.
We discuss the floating scum and sludge layer thicknesses and their measurement for evaluating the septic tank net free area and overall condition.
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.
How the Septic Tank Scum Layer or Sludge Layer Determine Pumpout Need
A Photographic Guide to Pumping a Septic Tank
This article series provides a step by step, photo-illustrated guide to opening, pumping, and inspecting septic tanks,
how a conventional septic tank is
located, opened, pumped out, cleaned, and inspected. This guideline is intended for septic pumping tank truck
operators and as general information for homeowners or septic service companies concerned with septic system care.
Readers should see Septic Tank Pumping Frequency Guide for a table explaining when to schedule a septic cleanout. Citation of this article by reference to this website and brief quotation for the sole purpose of review are permitted. Use of this information at other websites, in books or pamphlets for sale is reserved to the author. Technical reviewers are welcome and are listed at REFERENCES.
How to Determine If and When a Septic Tank Needs to Be Pumped
Standard Method 1: Pump the septic tank based on usage level - using the septic tank pumping tables
The most common method used to determine when a septic tank should be pumped is to use a tank pumping frequency table
which suggests the tank cleanout interval as a function of tank size and the level of usage of the system, such as the number
of occupants in the building.
We provide a table to give a septic pumping schedule at SEPTIC TANK PUMPING SCHEDULE.
Refer to the table to see the recommended pumping frequency for the particular septic system being considered.
For example, (from the septic tank pumping table), a 1000 gallon septic tank serving a home with five occupants
should be cleaned out about every two years. If the tank has only a 500 gallon capacity, it needs to be cleaned
about every six months!
Why a septic tank pumping table may be wrong - other septic tank pumping schedules
Septic tank shape affects its pumping needs.
What septic tank pumping tables may not recognize is the effect of tank shape on the need to pump it out.
Most septic tanks are 4ft. to 6ft. deep. But if the tank in question is a "low boy" or shallow septic tank
(used in areas where there is not enough soil depth to bury a conventional septic tank) it may need to be
pumped more often.
Septic tank usage affects its pumping schedule.
Septic tank pumping tables presume a number of occupants based usually on the number of bedrooms in a home. If your home has more occupants or other reasons for heavier septic system use the tank needs to be pumped more often.
Alternative Method 2: Use actual septic tank conditions to decide its next pump out time
By inspecting the conditions in the tank at pumping time you can decide if your septic tank should be pumped more or less often than called for in the pumping schedules. The thickness of the floating scum layer and bottom sludge layer determine how much net free area remains in the septic tank. The size of the net free area in the septic tank in turn determines
the EFFLUENT RETENTION TIME - which means that we want effluent to stay in the tank long enough for new solids and greases to separate out before effluent leaves the septic tank.
The exact point at which a septic tank needs to be pumped could be determined by opening the septic tank and
measuring the sludge and scum levels in the tank. As long as the sludge and scum layers are minimal (just a few
inches of thickness) or in other words, as long a the "net free area" in the tank (see below) is adequate,
the tank does not need to be pumped.
Depending on the size of the tank and its dimensions, as the sludge and scum layers become thick the net free
area remaining in the tank becomes so small that there is inadequate time for solids to separate into sludge and scum layers.
At this point, even though the septic system appears to be "working" its remaining life is in jeopardy because suspended
solid waste is being pushed into the drain field.
The volume of net free area in a septic tank determines the time available for this solid and grease separation. That
time is referred to as "septic effluent retention time." Short effluent retention time means that the tank sewage
remains agitated which in turn means floating and suspended solids are being pushed into and thus are clogging the drain field.
Method 3: there are other reasons people pump septic tanks
There are other reasons besides time or sludge/scum layer thickness that lead people to pump septic tanks out, such as diagnosing septic system problems, odors, backups, or inspecting / repairing septic tank baffles.
Try the search box below or CONTACT US by email if you cannot find the answer you need at InspectApedia.
when does a 900 gallon septic tank need pumping
(Aug 9, 2011) A home owners question said:
I had my septic tank inspected recently by a pumping company and was advised that the tank "should" be pumped (was recommended). The 900 gallon tank was pumped three years ago. The result of the inspection showed one (1)inch sludge and two (2)inch scum. I don't know what the criteria is as to when a tank requires pumping. Can anybody tell me what the criteria is when a 900 gallon tank requires pumping?
Reply: it's not just the tank volume, it's the tank dimensions that we look at to see the net free area of effluent
H.O. that was very little sludge and scum thickness. Based on those levels, if your usage level remains the same, you can pump less often. Please take a look at SEPTIC TANK PUMPING SCHEDULE for a table of septic tank pumping frequency recommendations based on tank size and number of occupants in the building.
It's always safer (and more profitable) for a pumping company to say "pump the tank every year..." or whatever, but you should be fine if you start with the pumping frequency in the recommended table, adjusting the actual pumping rate up or down in frequency based on the scum and sludge layer thickness observed each time the tank is pumped.
(Aug 11, 2011) "A home owner's" response. said:
Thanks ... for your advise. My wife and I are permanent occupants of our house (year around residence) and it seemed to me that the sludge or scum depth did not warrant the pumping of the tank except that the pumping company believes that a client may not know when a tank needs pumping therefore "recommends" pumping. The tank is gravity fed and I am treating the it monthly with enzyme in order to keep the drain field "healthy / operable. I have two subsequent questions and would appreciate receiving your advice.
(1)Based on the same tank capacity and same usage/load does a "single compartment" tank requires more frequent pumping than a "two compartment" tank?
(2)Is there a diffence between the performance of a "single compartement" tank and that of a "two compartment" tank?
You don't need septic treatments, and some can be harmful or even illegal, depending on where you live. Pumping the tank on schedule is the No. 1 thing you can do to extend drainfield life. Plus being sure groundwater is not flooding the fields.
Good questions 1 and 2. I haven't seen an answer phrased quite as you ask. In general a 2 compartment tank does a better job of separating sludge from effluent, and is more necessary with some designs such as aerobic systems. But it's the tank size or volume, total size, combined with usage that chiefly determines pumping frequency.
I could SPECULATE that in a 2-compartment tank of the SAME TOTAL CAPCACITY as a one-compartment tank, while the 2-compartment version is generally a superior design, as it improves sludge and scum separation from the effluent and thus extends drainfield life (you can also get this benefit with a septic tank outlet filter).
But this tank might have smaller volume to retain solids and thus might need more frequent pumping.
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Septic Tank/Soil-Absorption Systems: How to Operate & Maintain [ copy on file as /septic/Septic_Operation_USDA.pdf ] - , Equipment Tips, U.S. Department of Agriculture, 8271 1302, 7100 Engineering, 2300 Recreation, September 1982, web search 08/28/2010, original source: http://www.fs.fed.us/t-d/pubs/pdfimage/82711302.pdf.
Pennsylvania State Fact Sheets relating to domestic wastewater treatment systems include
Pennsylvania State Wastewater Treatment Fact Sheet SW-161, Septic System Failure: Diagnosis and Treatment
Pennsylvania State Wastewater Treatment Fact Sheet SW-162, The Soil Media and the Percolation Test
Pennsylvania State Wastewater Treatment Fact Sheet SW-l64, Mound Systems for Wastewater Treatment
Pennsylvania State Wastewater Treatment Fact Sheet SW-165, Septic Tank-Soil Absorption Systems
Document Sources used for this web page include but are not limited to: Agricultural Fact Sheet #SW-161 "Septic Tank Pumping," by Paul D. Robillard and
Kelli S. Martin. Penn State College of Agriculture - Cooperative Extension, edited and annotated by
Dan Friedman (Thanks: to Bob Mackey for proofreading the original source material.)
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
Advanced Onsite Wastewater Systems Technologies, Anish R. Jantrania, Mark A. Gross. Anish Jantrania, Ph.D., P.E., M.B.A., is a Consulting Engineer, in Mechanicsville VA, 804-550-0389 (2006). Outstanding technical reference especially on alternative septic system design alternatives. Written for designers and engineers, this book is not at all easy going for homeowners but is a text I recommend for professionals--DF.
Builder's Guide to Wells and Septic Systems, Woodson, R. Dodge: $ 24.95; MCGRAW HILL B; TP;
Quoting from Amazon's description: For the homebuilder, one mistake in estimating or installing wells and septic systems can cost thousands of dollars. This comprehensive guide filled with case studies can prevent that. Master plumber R. Dodge Woodson packs this reader-friendly guide with guidance and information, including details on new techniques and materials that can economize and expedite jobs and advice on how to avoid mistakes in both estimating and construction. Chapters cover virtually every aspect of wells and septic systems, including on-site evaluations; site limitations; bidding; soil studies, septic designs, and code-related issues; drilled and dug wells, gravel and pipe, chamber-type, and gravity septic systems; pump stations; common problems with well installation; and remedies for poor septic situations. Woodson also discusses ways to increase profits by avoiding cost overruns.
Country Plumbing: Living with a Septic System, Hartigan, Gerry: $ 9.95; ALAN C HOOD & TP;
Quoting an Amazon reviewer's comment, with which we agree--DF:This book is informative as far as it goes and might be most useful for someone with an older system. But it was written in the early 1980s. A lot has changed since then. In particular, the book doesn't cover any of the newer systems that are used more and more nowadays in some parts of the country -- sand mounds, aeration systems, lagoons, etc.
US EPA Onsite Wastewater Treatment Systems Manual [online copy, free] Top Reference: US EPA's Design Manual for Onsite Wastewater Treatment and Disposal, 1980, available from the US EPA, the US GPO Superintendent of Documents (Pueblo CO), and from the National Small Flows Clearinghouse. Original source http://www.epa.gov/ORD/NRMRL/Pubs/625R00008/625R00008.htm Onsite wastewater treatment and disposal systems,
Richard J Otis, published by the US EPA. Although it's more than 20 years old, this book remains a useful reference for septic system designers.
U.S. Environmental Protection Agency, Office of Water Program Operations; Office of Research and Development, Municipal Environmental Research Laboratory; (1980)
"International Private Sewage Disposal Code," 1995, BOCA-708-799-2300, ICBO-310-699-0541, SBCCI 205-591-1853, available from those code associations.
"Manual of Policy, Procedures, and Guidelines for Onsite Sewage Systems," Ontario Reg. 374/81, Part VII of the Environmental
Protection Act (Canada), ISBN 0-7743-7303-2, Ministry of the Environment,135 St. Clair Ave. West, Toronto Ontario M4V 1P5 Canada $24. CDN.
Manual of Septic Tank Practice, US Public Health Service's 1959.
Onsite Wastewater Disposal, R. J. Perkins;
Quoting from Amazon: This practical book, co-published with the National Environmental Health Association,
describes the step-by-step procedures needed to avoid common pitfalls in septic system technology.
Valuable in matching the septic system to the site-specific conditions, this useful book will help you install a reliable system in
both suitable and difficult environments. Septic tank installers, planners, state and local regulators, civil and sanitary engineers,
consulting engineers, architects, homeowners, academics, and land developers will find this publication valuable.
Onsite Wastewater Treatment Systems, Bennette D. Burks, Mary Margaret Minnis, Hogarth House 1994 - one of the best septic system books around, suffering a bit from small fonts and a weak index. While it contains some material more technical than needed by homeowners, Burks/Minnis book on onsite wastewater treatment systems a very useful reference for both property owners and septic system designers.
Septic Tank/Soil-Absorption Systems: How to Operate & Maintain [ copy on file as /septic/Septic_Operation_USDA.pdf ] - , Equipment Tips, U.S. Department of Agriculture, 8271 1302, 7100 Engineering, 2300 Recreation, September 1982, web search 08/28/2010, original source: http://www.fs.fed.us/t-d/pubs/pdfimage/82711302.pdf
Septic System Owner's Manual, Lloyd Kahn, Blair Allen, Julie Jones, Shelter Publications, 2000 $14.95 U.S. - easy to understand, well illustrated, one of the best practical references around on septic design basics including some advanced systems; a little short on safety and maintenance. Both new and used (low priced copies are available, and we think the authors are working on an updated edition--DF.
Quoting from one of several Amazon reviews: The basics of septic systems, from underground systems and failures to what the owner can do to promote and maintain a healthy system, is revealed in an excellent guide essential for any who reside on a septic system. Rural residents receive a primer on not only the basics; but how to conduct period inspections and what to do when things go wrong. History also figures into the fine coverage.
Grass is Always Greener Over the Septic Tank, Bombeck, Erma: $ 5.99; FAWCETT; MM;
This septic system classic whose title helps avoid intimidating readers new to septic systems, is available new or used at very low prices.
It's more entertainment than a serious "how to" book on septic systems design, maintenance, or repair. Not recommended -- DF.
US EPA Onsite Wastewater Treatment Systems Manual Top Reference: US EPA's Design Manual for Onsite Wastewater Treatment and Disposal, 1980, available from the US EPA, the US GPO Superintendent of Documents (Pueblo CO), and from the National Small Flows Clearinghouse. Original source http://www.epa.gov/ORD/NRMRL/Pubs/625R00008/625R00008.htm
Water Wells and Septic Systems Handbook, R. Dodge Woodson. This book is in the upper price range, but is worth the cost for serious septic installers and designers.
Quoting Amazon: Each year, thousands upon thousands of Americans install water wells and septic systems on their properties. But with a maze of codes governing their use along with a host of design requirements that ensure their functionality where can someone turn for comprehensive, one-stop guidance? Enter the Water Wells and Septic Systems Handbook from McGraw-Hill. Written in language any property owner can understand yet detailed enough for professionals and technical students this easy-to-use volume delivers the latest techniques and code requirements for designing, building, rehabilitating, and maintaining private water wells and septic systems. Bolstered by a wealth of informative charts, tables, and illustrations, this book delivers: * Current construction, maintenance, and repair methods
* New International Private Sewage Disposal Code
* Up-to-date standards from the American Water Works Association
Wells and Septic Systems, Alth, Max and Charlet, Rev. by S. Blackwell Duncan, $ 18.95; Tab Books 1992. We have found this text very useful for conventional well and septic systems design and maintenance --DF.
Quoting an Amazon description:Here's all the information you need to build a well or septic system yourself - and save a lot of time, money, and frustration. S. Blackwell Duncan has thoroughly revised and updated this second edition of Wells and Septic Systems to conform to current codes and requirements. He also has expanded this national bestseller to include new material on well and septic installation, water storage and distribution, water treatment, ecological considerations, and septic systems for problem building sites.
Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. Tel: (416) 964-9415 1-800-268-7070 Email: firstname.lastname@example.org. The firm provides professional home inspection services & home inspection education & publications. Alan Carson is a past president of ASHI, the American Society of Home Inspectors. Thanks to Alan Carson and Bob Dunlop, for permission for InspectAPedia to use text excerpts from The Home Reference Book & illustrations from The Illustrated Home. Carson Dunlop Associates' provides extensive home inspection education and report writing material.
The Illustrated Home illustrates construction details and building components, a reference for owners & inspectors. Special Offer: For a 5% discount on any number of copies of the Illustrated Home purchased as a single order Enter INSPECTAILL in the order payment page "Promo/Redemption" space.
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The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume.
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Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on these courses: Enter INSPECTAHITP in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
The Horizon Software System manages business operations,scheduling, & inspection report writing using Carson Dunlop's knowledge base & color images. The Horizon system runs on always-available cloud-based software for office computers, laptops, tablets, iPad, Android, & other smartphones