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Blocked drain or drain backup diagnosis: caused by drain blockage versus caused by septic system failure: here we explain how to determine if a blocked or slow drain is due to a problem inside the building or outside in a sewer line or failing septic system.
When a building drain or main sewer line is clogged or slow, or when there is a septic system backup, it's important
to determine where the problem lies, since the repair steps can be quite different and costs can vary widely.
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.
DRAIN vs SEPTIC - Is the slow drain problem due to indoor plumbing or the septic system?
Is it a Plumbing Problem or a Septic System Problem - A First Look
Sewage odors, wet areas on the property, slow fixture drains, gurgling drain noises, or plumbing fixtures which
"back up" or overflow back into the building may be the first signs of trouble at a property. Image courtesy Carson Dunlop Associates.
[Click to enlarge any image]
If there are sewage odors or soggy sewage-smelling wet areas at a property, the on-site waste disposal system
is likely to be at fault. Even so, without further investigation we don't know yet if the problem is a simple
repair such as a broken pipe underground, or a costly failure such as a saturated absorption field.
If building drains are slow or clogged, the problem could be the in-building plumbing drain-waste-vent (DWV) system
or there may be a problem with the septic system. Without further investigation we don't know.
these clues (and articles about them) that assist in diagnosing clogged drains, drain backups, and septic or sewage odors:
TOILET REPAIR GUIDE - how to fix a clogged or poor-flushing toilet - the problem could be the toilet or its controls, not the drain itself
A simple initial step
must be taken to distinguish between an in-building plumbing problem and an (outside) on-site waste disposal
Simply put, if a single building fixture is sluggish or clogged, but if other building fixtures
drain properly, you should suspect a local clog or vent problem at the individual fixture.
If all building drains are slow or clogged,
or if waste is backing up into the building from the lowest plumbing fixture, you would suspect the sewe line is blocked or there is a failing or blocked onsite waste disposal system (septic system).
Our client (left) is pointing to a leaky clamp patch on a building drain line. Odd and excessive slope, a mix of materials, and this patch were evidence of amateur workmanship that presaged problems with this drain system.
Curtain Drain - Design Sketch for Protecting Drainfields from Wet Soils
Inspect the septic system absorption field: if the drain field (synonyms: leach field, leaching bed, soakbed, absorption bed, seepage bed, seepage trench) is wet or smelly we suspect a septic absorption field failure.
If the absorption fields
are properly installed there is adequate clearance, typically 4.5 ft. between the bottom of the field and the top of the seasonal (spring)
high water table on the property.
Otherwise in wet weather conditions your field is flooded, cannot readily accept effluent from the tank,
and worse, you're also contaminating the local groundwater with pathogens from the septic tank.
If your absorption field is on a slope and is
subject to high levels of surface or subsurface runoff, you may need to install an intercept drain or curtain drain (sketch above, source US EPA) up-slope from the
Keep the intercept drain or curtain drain at least 10 meters from the absorption field perimeter. If the field is flooded and you do not have
problems with surface runoff, subsurface runoff, or high water table, before you assume that the field is at the end of its life, check for
constantly running plumbing fixtures such as running toilets or a water softener which is stuck in its "backwash" cycle.
If exploration of the on-site waste disposal system piping from house to tank, tank to distribution box, and
distribution box to drainfield indicates that the failure is in the drainfield (or absorption system), a more
extensive system repair is needed and significant costs are likely to be incurred.
Also see CAMPING & EMERGENCY TOILETS and also see TOILET ALTERNATIVES for a discussion of camping toilets, chemical toilets, emergency-use toilets, waterless toilets, graywater systems, composting toilets, home health care toilets, incinerating toilets, outhouses, and latrines.
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Questions & answers about how to tell the difference between a clogged drain line and a blocked, clogged, or failed septic system, posted originally a this article are now found at CLOGGED DRAIN vs SEPTIC BLOCKAGE FAQs
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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.
Operation & Maintenance Manual for Septic Tank Drainfield Sewer Systems, Missoula MT: NOrthern Region, Environmental Health Engineering, Forest Service, U.S. Department of Agriculture, August 1981. Cited by the above reference.
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.)
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.
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
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.
TECHNICAL REFERENCE GUIDE to manufacturer's model and serial number information for heating and cooling equipment, useful for determining the age of heating boilers, furnaces, water heaters is provided by Carson Dunlop, Associates, Toronto - Carson Dunlop Weldon & Associates Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on any number of copies of the Technical Reference Guide purchased as a single order. Just enter INSPECTATRG in the order payment page "Promo/Redemption" space.
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.
Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
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