Sewer Line Installations on Steep Slopes InspectAPedia® -
How to install sewer or septic lines & piping at steep sites
Proper drain line slope is important in avoiding septic or sewer line clogging and backups
Zig-Zag septic piping on steep hillsides
U-turn septic piping on steep hillsides
Septic piping along the fall line of a slope
Steep septic designs used for sewer or septic piping replacement or new installations
Questions & answers about sewer or septic piping lines on steeply sloped sites
Sewer line installation or replacement on steep slopes: This article describes the installation of drain lines on steep slopes between a house and the septic tank. We present an actual case study, illustrated with photos of each step in the diagnosis and replacement of a blocked
sewer line.
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Also see STEEP SLOPE SEPTIC DESIGNS. Technical reviewers are welcome and are listed at "References." 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.
Guide to installing the replacement sewer pipe line at Steep Sites
What is the proper slope or pitch for a drain waste pipe? When wastewater flows at the correct speed in a drainpipe, the water carries the solid waste, feces and toilet paper, for example, along with the water out to the septic tank or sewer mains. Plumbing codes and wastewater piping guides commonly specify that building drains should be pitched at 1/8" to 1/4" of slope per foot of linear run or distance.
Problems with steep drops between house and septic tank: But at a steep building site such as the property shown in our page top photograph, the drop in elevation between a building main drain and the septic tank inlet opening (or sewer main connection) may be so much that the slope of the waste piping will exceed the recommended limits for slope.
When installing a building drain line for wastewater, the wastewater flow rate we want is 2 feet per second. If waste flows in the sewer line faster than 2 fps, the risk is that water leaves the solids behind in the pipe where clogs may be recurrent.
If waste flows in a septic or sewage drain line more slowly than the desired speed, the risk is that is that listless flow leaves sewage which blocks the pipe.
ZigZagging Drain Line Piping Down a Slope
One approach to achieving the proper wastewater flow rate in a drain line down a steep slope would be to zigzag the pipe down the slope, making numerous turns. My OPINION is that the added turns and length of this approach may increase the chances of future sewer line blockages, the zigzag drain line approach will also make it more difficult to clean out blockages, or you will need to add sewer line cleanout access points at every run and turn in the installation.
In short, a zigzag pipe run down a slope costs more, has more turns that risk clogging, is harder to clean out, takes up a lot more space on the site, and is usually not installed by contractors.
Straight-run Drain Line Piping Down a Steep Drop Slope between House and Septic Tank or Sewer Main
My experience is that many waste line installers simply install a straight sewer line from house to septic tank or house to sewer main, regardless of the building slope, provided that we have at least 1/8" per foot, preferably 1/4" per foot, or more.
Lower slope or nearly-flat drain lines are more likely to clog. On that side topic, if you're installing a drain line that may be sloped too little and you cannot easily remedy the situation, be sure to install extra cleanout access ports.
Experience in Installing Steep Sewer Drain Line Piping
Steep Drain Slopes May be Tolerable
My OPINION is that if the total pipe run is steeper than what's normally specified, you might never see a blockage
At the property shown in these photos and in the other photos in this series on sewer line replacement, the sewer line drops on a slope between 2” and 3” per foot over a 40 foot run between house exit line and septic tank inlet baffle. This house-to-septic tank drain piping should be in the “danger zone” of leaving solids behind liquids during a toilet flush
But having managed this property for more than twenty years, we can say with confidence that we never had a problem with too-fast drainage blocking the waste line. Blockages did not occur when the original waste pipe was constructed of jointed clay pipe. Sewage blockages have not occurred since we replaced the original clay with plastic piping
I suspect that plastic drain piping is more slippery inside and has fewer joints to serve as obstructions, further reducing the chance of a blockage. The only problem we had with the line was when the old clay line was crushed and then blocked by mud
SO if you use plastic piping, straight runs, good smooth joints, you will probably be ok
Other Steps to Avoid Problems with Septic or Sewer Drain Lines on Steep Sites
Septic or Sewer Drain Line Cleanouts: For convenience I’d add outdoor cleanout access ports to the sewer line every 20’ or so
Proper septic pipe connections: Make sure that the new piping connections are made correctly, lubricated and fully seated during assembly. In our photo at left the grease helps assemble the plastic sewer piping joint. The black line on the right hand pipe section tells the installer when the pipe sections have been fully joined.
Proper sewer pipe directions: The receiving pipe hub or "female" end of the pipe is the next downhill section. Don't do this backwards or you invite leaks or clogging in your sewer line
Use smooth drain line connections: the hub-less drain pipe connector shown in our photo at left was used to connect the new plastic waste line (running downhill to the septic tank) to the old cast iron waste line at its point of exit from the building.
It was important that these pipes be properly aligned (to avoid leaks at the connector) and that the connection and pipe ends be filed smooth to minimize the chances of waste line blockages at this point in the system.
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Installing Septic Drainfield Piping on Steep Slopes is a Different Matter Entirely
Just to be clear, in this article we've discussed the installation of solid piping between a building and its septic tank or sewer main and we've said that steeper slopes may be ok.
But the possible "OK" for steep drain piping does not in any way apply to the perforated piping installed in a septic drainfield gravel trench.
Readers concerned with septic installation advice for steeply sloped or rolling sites should see these articles:
Sewer or Septic Line Installation at Steep Sites which describes sewer piping between a building and septic tank or sewer main at steep sloped sites which slope down significantly between the building and the septic tank.
DOSING SYSTEMS PRESSURE which describes pressure dosing systems that may be useful for disposing of septic effluent at steep sites where the drainfield must be located either uphill or downhill from a septic tank or building.
GRAVELLESS SEPTIC SYSTEMS- some gravelless systems can handle gentle curves necessary to follow rolling slope lines
Pumps Septic pumps, sewage ejector pumps, grinder pumps, effluent pumps, sump pumps, & septic pumping stations, septic pump alarms - systems that will be needed if a building or septic tank are lower than the drainfield or sewer main.
STEEP SLOPE SEPTIC DESIGNS which describes installation of septic drainfields on steep or rolling sites.
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Thanks to Thomas Gleason, excavators, Poughkeepsie, NY 845-454-3730, for the excavating work at the project photo documented here in September 2006
Thanks to Cleveland Plumbing, the prime plumbing contractor, Staatsburgh, NY 845-485-7700 for the plumbing work and drain clog diagnosis work documented here in September 2006
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.
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), Advanced Onsite Wastewater Systems Technologies.
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 we recommend for professionals--DF.
AEROBIC SEPTIC SYSTEMS
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.
Design Manuals for Septic Systems
US EPA Onsite Wastewater Treatment Systems Manua [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 Books
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. (DF volunteers to serve as indexer if Burks/Minnis re-publish this very useful volume.)
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. We refer to it often.
While Minnis says the best place to buy this book is at Amazon (our link at left), you can also see this book at Minnis' website at http://web page .pace.edu/MMinnisbook
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
Planting Over Septic System Component", Daniel Friedman (author/editor, InspectAPedia.com), The Innovator, Winter/Spring 2008, BCOSSA, British Columbia OnSite Sewage Association, 201-3542 Blansard St., Victoria BC V8X 1W3 Canada
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.
Test Pit Preparation for Onsite Sewage Evaluations, State of Oregon Department of Environmental Quality, Portland OR, 800 452-4011. PDF document. We recommend this excellent document that offers detail about soil perc tests, deep hole tests, safety, and septic design. Readers should also see Soil Percolation Tests and for testing an existing septic system, also see Dye Tests
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.
The NSFC Products List has an excellent list of design manuals/modules available from their website or by telephone 800-624-8301
Submissions welcome. send us a suggested document link or request an exchange of website links
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