Diagnosing Clogged Drains & Septic System Backups: Is it a blocked drain or the septic system? - A First Step for Homeowners
InspectAPedia® -
How to Diagnose & Repair a Clogged Plumbing Drain
How to un-clog a blocked drain yourself and when to call a plumber
How to Diagnose a Septic System Backup
How to Diagnose a Failed Septic System
Sketch for curtain drain to protect a drainfield from wet soils
Table of diagnostic steps for wet soil areas around sewer pipes or septic drainfields
Questions & answers about how to diagnose & repair slow or clogged building drains
This article series explains how to troubleshoot & repair slow or blocked drains, diagnose & fix septic system backups & how to distinguish between a probable septic system failure versus a probable blocked building drain or sewer line.
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.
InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers nor with topics or services discussed at this website.
FIRST SIGNS - What are the First Signs of Trouble Indicating Failure of a Septic System?
What should a building owner do if the building drains stop working or there are odors or sewage-suspect wet areas on
the property? It is important to distinguish between a simple blocked trap or blocked pipe and a failing septic system.
That's because the remedies, as well as the costs, are quite different.
The photo at page top shows the final repair for a toilet that was backing up - in this case the drain was blocked by
a child's underpants. (See TOILET REPAIR GUIDE.) By following the investigative steps we recommend you can determine the difference between
a blocked drain and other more extensive plumbing or septic system problems.
Our photo at left shows a clogged shower drain in an older home. That white blob of crud in the drain trap may be removed or pushed through by a plumbing snake. But if the building is served by galvanized drain lines, those may be blocked internally by rust or mineral deposits, leading to a more costly repair.
Readers should 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.
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.
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.
Also see
these articles that assist in diagnosing clogged drains, drain backups, and septic or sewage odors
Drain Noises: may indicate defective or clogged plumbing: how to diagnose and cure drain sounds
SEWER GAS ODORS - a step by step guide to tracking down where smells and sewer gas odors are coming from
Sewage Odors in Wet or Cold Weather - Septic Odors or Sewage Odor Diagnosis & Repair Guide for diagnosing and eliminating cold weather sewer gas odors
TOILET REPAIR GUIDE - how to fix a clogged or poor-flushing toilet; other toilet problem repairs are also discussed.
DRAIN vs SEPTIC - Is the slow drain problem due to indoor plumbing or the septic system?
A simple initial step
must be taken to distinguish between an in-building plumbing problem and an (outside) on-site waste disposal
system problem.
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 onsite waste disposal 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.
BLOCKED Building Plumbing DRAIN? - Is the problem a blocked drain or pipe or the whole septic system? How to Find and Fix a Blocked or Slow Building Plumbing Drain.
Here are the steps to take, in order, to deal with a clogged or slow drain. In the process we'll discover
if the problem is only a blocked pipe or if the septic system is at fault. Before digging up the septic
system be sure to go through these steps - it may save you some money.
Check several building plumbing fixtures: Refining the above procedure,
if the main building drain is clogged, or if the on-site waste disposal system
is blocked, fixtures on upper floors in a building may appear to drain normally, while fixtures on lower floors
or at the lowest level in the building may not drain at all, or may even overflow back into the building when upper
floor fixtures are operated. If the problem is just at a toilet see TOILET REPAIR GUIDE for how to diagnose and repair toilet flush, fill, noise, drain, odor, sound, running problems of all kinds.
Check the history of the slow drain problem: if the drain has always been slow, we suspect a plumbing problem such as improper venting, a drain installation error, or a problem with the individual fixture since the day it was installed (such as a poor flushing toilet). If the drain used to work but has become slow, we suspect a plumbing drain/waste/vent system blockage has developed, or if the building is connected to a private septic system, that could be failing or blocked.
How to Try to clear A Blocked Plumbing Drain by Yourself
There are some simple do-it-yourself drain clearing steps that you may want to try before going further in your investigation or hiring of an expert. The four drain clearing methods listed below are discussed in detail at BLOCKED DRAIN REPAIR METHODS.
Clear a blocked sink trap: before messing with snakes, wires, plungers, and plumbers, if the blockage is at a single sink or tub trap look into the trap with a flashlight. Use a toilet plunger to clear a simple blocked drain. Use a plumbing snake to clear a blocked drain Use a kinetic water ram [Amazon.com] to clear a blocked drain
Call a professional plumber to clean individual fixture drain:
A reasonable approach at this point is to call a plumber specializing in drain cleaning. By opening and
attempting to clean the building drain or fixture drains, an experienced plumber can determine if the problem
is with the building DWV system (drain waste vent) or if it's an outside problem. But before calling the plumber here are the simple do it yourself basics for clearing a clogged building drain. If these work you may be back in business.
If the drain clearing effort is unsuccessful, you will have paid the plumber for his/her time and also you should ask for that expert's diagnostic assistance. If the drain problem is more than a simple intermittent blockage, what is the problem?
Check the house drain-vent system: if there is not an obvious drain blockage, and if drains are slow, particularly if you hear a
"gurgling" sound at fixtures during draining, I'd suspect that the building vent system is incomplete, improperly installed, or has become
blocked (perhaps by an animal or an insect nest, or in northern climates, by snow if the above-roof extension is too short, or
by ice if the vent is too small in diameter - rising steam condenses and freezes in the outside portion of the vent).
If the
drain problems occur only in freezing weather or when there is heavy snow, I'd suspect these latter defects. If you hear a gurgling
at the sink when the toilet is flushed this might be the case. Have a plumber inspect and test the vent system. Blocked vents do not
usually cause drain backup but they will cause slow draining.
Also see
Drain Noises: may indicate defective or clogged plumbing: how to diagnose and cure drain sounds, and
Sewage Odors in Wet or Cold Weather - Septic Odors or Sewage Odor Diagnosis & Repair Guide for diagnosing and eliminating cold weather sewer gas odors.
If the in-building DWV piping is not blocked, and if the drain line between the building and septic tank (or equivalent
component such as a cesspool) is not blocked, and if in-building drains are slow or blocked, the problem is most-likely in
the on-site waste disposal system.
Even if the problem appears to be "outside" of the building, you still have not determined whether the problem there
is a blocked or damaged drain line or a more extensive failure of the onsite waste disposal system. This is a very
important distinction. Un-clogging a drain line, or excavating and repairing a crushed or broken drain line outside
the building is typically a much less costly repair than replacement of a septic tank, drain field, or seepage system.
If the problem is in the on-site waste disposal system, additional inspection and testing are needed to
determine the nature of the failure. Again, a blocked drain line exiting a septic tank, or a failure in the
distribution box (connecting the septic tank to the network of drainfield lines, seepage pits or galleys) the
repair needed may be local and modest in expense.
Snake (clean) the building drain between house and septic tank: this will check for obstructions, roots, and collapse
in the line between house and tank
and will also, if you don't already know, determine the probable distance from the house to the septic tank.
If you're seeing recurrent
blockages in a buried waste line, I'd suspect that it may be improperly sloped, or that the pipe may have been partly broken by vehicle
traffic, or that it's partly blocked by a tree root or debris. An experienced drain cleaning professional can often tell by the "feel" of
the plumbing snake just what kind of obstruction has been encountered.
Open and inspect the septic tank: if the intake or outlet drains from the tank are blocked because of floating scum or high sludge
in the tank, the tank needs to be cleaned. Call a septic tank pumping company. But beware: if scum or sludge levels in the tank were excessive,
you've been pushing solids into the absorption system and you may have reduced the remaining life of that component. If the baffles are
damaged they should be replaced.
If your building is connected to a municipal sewer (not to a private septic system) there may be a blockage in or damage to the sewer line between your building and the sewer main. You might also check with your local water and sewer municipal department to be sure that there is not a temporary stoppage in the main sewer. The sewer line between an private building and the public sewer main is the responsibility of the property owner to maintain and repair, but you may need permission from your municipality before you can excavate or make other repairs.
Find and inspect the distribution box: if the tank is clear and its inlet and outlet not blocked, and if drains are backing up in the house I'd expect the
liquid level in the tank to be abnormally high and I'd be looking for a blockage in the absorption system, or a soil absorption system failure.
The distribution box (or boxes) connect the tank outlet to multiple leach lines, seepage pits, or other soil absorption system(s) (if more than
one is present). Look in the D-box. If the box has been flooding and all of the outlets from it are equally distributing effluent, the absorption system is blocked
or in failure. But if the box is tipped or otherwise misadjusted so that effluent is not being distributed evenly across the absorption
system sub components, that defect should be corrected. However I would not expect a tipped D-box to lead to drain backup in the building.
Curtain Drain - Design Sketch for Protecting Drainfields from Wet Soils
Inspect the absorption field: if the field 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
absorption field.
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.
Plumbing Drain Clog & Wet Soils Septic System Troubleshooting Chart
Edited & expanded from original source: 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 (USDA), 8271 1302, 7100 Engineering, 2300 Recreation, September 1982
Watch out: disassembling old plumbing parts often means things fall apart. Don't try in-home plumbing repairs when stores selling repair parts are closed unless you have spare parts, tools, sealants, etc. on hand.
Watch out: Never lean over, smoke close to, nor ever enter a septic tank - the risk is rapid death. Also see SEPTIC & CESSPOOL SAFETY.
Drain Problem
Check in This Order
Clogged Drain Repair Action
A:
Toilet, tub, sink, shower drain slow or backs up
Clogged fixture trap - only the individual fixture is having a problem
Disassemble trap, remove clog; try a plumbing snake or kinetic water ram. Avoid heavy use of chemical drain cleaners. See BLOCKED DRAIN REPAIR METHODS
Clogged building drain piping - multiple fixtures may be slow or backed up, but unless clog is at main drain, other fixtures will be working ok.
Check for an outdoor cleanout access to see if water is standing in the pipe outside the building. If no water is found there, the blockage is inside the building. Try a plumbing snake; if no success you need a professional plumber. See BLOCKED DRAIN REPAIR METHODS
Clogged drain piping between building and septic tank - standing water in the pipe between building and septic tank; may also be a problem in the septic tank, D-box, or drainfield piping.
Often caused by roots in the drain line or a collapsed or broken or partly collapsed drain line. Frequent power-snake operation can break old drain piping; trees too close to the building or to piping, especially with older pipe designs are often invaded by tree roots.
To determine where to try reaming the drain line, inspect the septic tank wastewater level. In a two-chamber septic tank if the outlet chamber is above the outlet pipe, the problem is probably downstream from the septic tank.
If the waste level is at the outlet, or if you have a single-chamber septic tank, measure the scum and sludge levels. MEASURE SCUM & SLUDGE. If these levels are above the limit, pump the septic tank immediately.
If the septic tank inlet is clear, the pipe between building and septic tank is probably blocked and needs to be cleared. You need a professional plumber. See BLOCKED DRAIN REPAIR METHODS
See DRAIN vs SEPTIC for more help in distinguishing these blockages.
Clogged drain piping between septic tank and D-box or drainfield - no backup in pipe between building and septic, backup visible inside the septic tank.
As we described above, In a two-chamber septic tank if the outlet chamber is above the outlet pipe, the problem is probably downstream from the septic tank.
Broken drain line outside the building - rare but shallow pipes in cold climates can become blocked, freeze, and burst.
You need a professional plumber. Snaking the line may discover the location of the collapsed or broken piping. You need a professional plumber. See BLOCKED DRAIN REPAIR METHODS
Septic Dosing Systems - diagnosis, repair
B.
Septic Dosing Tank Not Draining
Check for clogged piping leaving the septic tank, at the D-box, or in the drainfield.
Check for an inoperative siphon or pump.
Check the siphon vent pipe to see if wastewater is flowing into it. If not see the two causes listed just above in this table.
If water is entering the siphon vent pipe see topic C. below
C:
Dosing siphon not working
Common problem, usually a cracked or broken siphon bell, siphon pipes, or a clogged pipeline exiting the tank
See "B" above. If wastewater is flowing into the vent pipe, pump the dosing tank & inspect/repair the siphon. A broken bell can block the siphon.
If the bell is undamaged, remove the bell and snake the siphon for blockage.
If the siphon is not damaged or blocked, see the final two diagnoses in "A" above.
If a blockage is found you need a professional plumber familiar with dosing system equipment.
If wastewater flows out of the dosing tank, pump the tank & inspect pipes & siphon components for damage you need a professional plumber to do this.
D: Dual dosing siphons not working
Alternating or dual siphons or tipping pans, caused by cracked or broken bell, pipes, or pipeline
Dual siphons occasionally may stop alternating as they should. The septic system may continue to appear to function but you may be overloading one portion of the drainfield. If siphons only rarely fail to alternate, it's not a significant concern .
If one of the siphons is not working at all, see "C" above.
E: Septic Effluent Breakout Diagnosis & Repair - Wet soils in the drainfield area, puddles, sewage odors
E.1. Wet soils along or near sewer piping
Look for a broken or cracked waste pipe in this area
Excavate gently, find the break, repair or replaced the damaged section. Diagnose the cause of the breakage: driving over the piping, frost damage to a clogged line, roots, buried rocks, poor original installation. Look for tree root invasion causing a break - you may need to remove nearby trees or shrubs.
E.2. Wet soils close to the septic tank or dosing tank
Broken or cracked pipe, cracked or damaged septic tank, or sewage backing up inside the septic tank.
Determine the cause as in "A" above - probably the problem is downstream from the septic tank. Start by finding and inspecting the Distribution box. If it's not flooded, the problem may be in the piping between the septic tank and the D-box. Otherwise the fields and field piping may be damaged or flooded. This may be an indicator of a septic field at end of life, improper installation, local groundwater flooding, etc.
E.3. Wet soils over or close to the drainfield or soakaway bed
Failed septic drainfield, temporarily overloaded drainfield, flooding by groundwater from other sources
At mound systems remember to inspect carefully around the lower edges of the mound, especially at the lowest end of the leach bed lines.
Inspect nearby ponds, streams, culverts, ditches.
Failure to pump septic tank increases the risk of a field failure;
Inspect for external sources of water around the drainfield and re-route, install a curtain drain, or take similar measures if this is the cause.
A septic dye test can help distinguish between septic effluent failure and a drainfield flooding due to local groundwater or surface runoff problems.
Note: In addition to drawing on the USDA document cited below, that source cites the National Park Service, U.S. Department of Interior as a cooperator who provided advice and suggestions for this content.
Critique, contributions wanted: Contact Us to suggest corrections or additions to articles at this website, and if you wish, to receive online listing and credit as a contributor. Particular thanks are due to the many experts and also consumers who read and critique technical articles at InspectAPedia.com.
Additional technical contributors & reference sources for this article are listed below.
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.)
...
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.
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.
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How to Try to clear A Blocked Plumbing Drain by Yourself
