Diagnosing Clogged Drains & Septic System Backups: Is it a blocked drain or the septic system? - A First Step for Homeowners InspectAPedia® -
How to Diagnose a Clogged 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
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This website explains how to investigate slow or blocked drains and septic system backups to distinguish between a probable septic system failure versus a probable blocked building drain.
When a building drain 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.
The photo above shows the final repair for a toilet that was backing up - in this case the drain was blocked by
a child's underpants. 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.
This document is a chapter of Inspecting, Testing, & Maintaining Residential Septic Systems.
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.
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 SEWER GAS ODORS - a step by step guide to tracking down where smells and sewer gas odors are coming from Drain Noises: may indicate defective or clogged plumbing: how to diagnose and cure drain sounds
Sewage Odors in Wet or Cold Weather - Septic Odors or Sewage Odor Diagnosis & Repair Guide for diagnosing and eliminating cold weather sewer gas odors
and for sewer or septic backups, see SEPTIC BACKUP PREVENTION and SEPTIC BACKUP REPAIR
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 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.
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 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.
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Kinetic water rams are described and demonstrated at waterram.com/faq.php
Thanks to Alan Carson and Bob Dunlop, Carson Dunlop, Associates, Toronto, for permission to use illustrations from their publication, The Illustrated Home which illustrates construction details and building components. Carson Dunlop provides home inspection education, publications, report writing materials, and home inspection services. Alan Carson is a past president of ASHI, the American Society of Home Inspectors.
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
Our recommended books about building design, inspection, and repair, and about indoor environment testing, diagnosis, and cleanup are at the InspectAPedia Bookstore.
SEWER GAS ODORS - how to find and cure sewer odors and septic odors in and around buildings
SEPTIC FAILIURE CAUSES in our Online Septic Book - Details Address: How Does Each Septic System Component Fail? - What to Look For During a Septic Inspection - Step by Step Diagnosis
More Information on Building Diagnostic Inspections and Repairs
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The Mold Information Center: What to Do About Mold in Buildings, When and How to Inspect for Mold, Clean Up Mold, or Avoid Mold Problems
Environmental Inspection, Testing, & Diagnosis On-Site IAQ, Gas, Air Testing, Mold Investigation, Sick Building Diagnosis, Lab Services, & Remediation Plan Preparation - indoor air quality testing, problem source determination, supporting lab work, written remediation plan addressing removal of environmental and other hazards and prevention of their recurrence.
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