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PLUMBING SYSTEM INSPECT DIAGNOSE REPAIR
AGE of PLUMBING MATERIALS & FIXTURES
AIR DISCHARGE at FAUCETS, FIXTURES
BACKDRAFTING HEATING EQUIPMENT
BACKFLOW PREVENTER VALVE, HEATING SYS
BACKFLOW PREVENTER, HEATER WATER FEEDER
BACKUP PREVENTION, SEPTIC
BACKUP PREVENTION, SEWER LINE
BACKWATER VALVES, SEWER LINE
BATH & KITCHEN DESIGN GUIDE
BLOCKED DRAIN REPAIR METHODS
CARBON MONOXIDE - CO
CHECK VALVES, WATER SUPPLY
CHLORINE IN SEPTIC WASTEWATER
CLEANOUTS, PLUMBING DRAIN
CLOGGED DRAIN DIAGNOSIS & REPAIR
CLOGGED SUPPLY PIPES, DIAGNOSIS
CLOGGED SUPPLY PIPES, REPAIR
CLOGGED SUPPLY PIPES, HOT WATER
CONDENSATION or SWEATING PIPES, TANKS
CROSS CONNECTIONS, PLUMBING
DEPTH of DRAIN & SEWER PIPES
DEPTH of SEPTIC TANK
DRAIN & SEWER PIPING
FLOOD DAMAGE ASSESSMENT, SAFETY & CLEANUP
FLOODED HEATING EQUIPMENT REPAIR
FLOODED SEPTIC SYSTEMS, REPAIR
FLOODED WATER HEATER REPAIR
FLOOR DRAIN / TRAP ODORS
FLUSHOMETER VALVES for TOILETS URINALS
GALVANIC SCALE & METAL CORROSION
GALVANIZED STEEL PIPING
HARD WATER - SOFTENERS
HEAT TAPES, Heat, Insulation prevent Freeze-Up
KITCHEN VENTILATION DESIGN
LEAD POISONING HAZARDS GUIDE
LEAD PIPES in buildings
LEAD in WATER, ACTION LEVEL & REMEDIES
LEAK TYPES, Water Supply/Drain Pipe
METHANE GAS SOURCES
MIXING / ANTI-SCALD VALVES
MVOCs & MOLDY MUSTY ODORS
NOISE CONTROL for PLUMBING
NOISE, PLUMBING DRAIN DIAGNOSIS
NOISE, PLUMBING DRAIN REPAIR
NOISE, PLUMBING CHECKLIST
NOISE, WATER HEATER
NOISES, WATER PUMP
ODORS GASES SMELLS, DIAGNOSIS & CURE
OUTHOUSES & LATRINES
PIPING IN buildings, Clogs Leaks Types
PLUMBING FIXTURES, KITCHEN, BATH
PLUMBING FIXTURE TRAPS
PUMPS, WATER REPAIR
REPAIR BURST LEAKY PIPES
SEWER GAS ODORS
SEPTIC METHANE GAS
SEPTIC SYSTEM ODORS
SEWAGE BACKUP, WHAT TO DO
SEWAGE BACKUP PREVENTION
SEWAGE BACKUP TEST & CLEANUP
SEWAGE CONTAMINATION in buildings
SEWAGE EJECTOR / GRINDER PUMPS
SEWAGE PUMP CLOG DAMAGE
SEWER GAS ODORS
SEWER LINE REPLACEMENT
SPAS, WHIRLPOOLS, SOAK/JETTED TUBS
SULPHUR & SEWER GAS SMELL SOURCES
SUMP PUMPS GUIDE
TOILETS, INSPECT, INSTALL, REPAIR
TRAPS on PLUMBING FIXTURES
TUBS & TUB REPLACEMENTS or RELINERS
WATER ODORS, CAUSE CURE
WATER PIPES, Clogs Leaks Types
WATER PRESSURE & FLOW MEASUREMENT
WATER PUMP REPAIR GUIDE
WATER QUANTITY IMPROVEMENT
WATER SHUTOFF VALVE LOCATION, USE
WATER SOFTENERS & CONDITIONERS
WATER SUPPLY & DRAIN PIPING
WATER TANK: USES, TROUBLESHOOTING
WATER TREATMENT EQUIPMENT CHOICES
WELLS CISTERNS & SPRINGS
WINTERIZE A BUILDING
This plumbing traps (interceptors) article describes plumbing traps (interceptors) and how to diagnose, find, and cure odors in buildings including septic or sewage or sewer gas smells or "gas odors" in buildings with a focus on homes with a private onsite septic tank but including tips for owners whose home is connected to a sewer system as well.
Green links show where you are. © Copyright 2013 InspectAPedia.com, All Rights Reserved.What makes the smell in sewer gas? Sewer gases are more than an obnoxious odor. The page top schematic of a typical plumbing trap is courtesy of Carson Dunlop'. Also see Wet Weather or Cold Weather Septic Odors or Sewage Odor Diagnosis & Repair Guide for additional odor tracing and cure advice for odors occurring during wet or cold weather.
Watch out: Because sewer gas contains methane gas (CH4) there is a risk of an explosion hazard or even fatal asphyxiation. Sewer gases also probably contain hydrogen sulfide gas (H2S) In addition some writers opine that there are possible health hazards from sewer gas exposure, such as a bacterial infection of the sinuses (which can occur due to any sinus irritation). Depending on the sewer gas source and other factors such as humidity and building and weather conditions, mold spores may also be present in sewer gases.
Technical note on sewer gas smells: because the "sulphur smell" that some people may associate with dangerous sewer gases can have other sources having nothing to do with building plumbing systems, readers should also see CHINESE DRYWALL HAZARDS and ODORS, SULPHUR SMELL SOURCES and ODORS, SEPTIC or SEWER and finally, ODORS & SMELLS DIAGNOSIS & CURE where we describe how to track odors to their source or cause.
What's the difference between Plumbing Traps vs Plumbing Interceptors?
Note: recent changes in plumbing codes including ASME Standards, the Uniform Plumbing Code (UPC), Canadian Standards Association (CSA) and the International Plumbing Code (IPC) have dropped the term plumbing trap, and substitute a more inclusive word, "interceptor".
In some building codes and plumbing texts you will see increased use of the term interceptor where you may be more familiar with the term plumbing trap. In particular, grease traps are referred to now as hydromechanical grease interceptors or gravity grease interceptors.
Common Plumbing Trap or Interceptor Defects
Here are some plumbing trap (interceptor) defects to check. Any of these can produce drainage problems and in turn may leak or cause sewer gas or septic odors to be produced in or even outside of a building:
Leaky, Missing, or Improperly Mounted/Located Plumbing Traps / Interceptors
Inspect the building plumbing traps for leaks, defects or improper or missing traps:
The photo shows a plumbing "trap" that is guaranteed to produce odors: it's not a plumbing trap at all, but rather this plumbing drain uses a car radiator hose.
This home made drain pipe also leaks, as you can see by the black mold on paper located below the sink.
Definition & Issues with S-Traps on Plumbing Fixtures & Drains
Use of "S" Traps or other illegal and obsolete plumbing fixture traps where a "P" trap is required. S-traps are often installed in older buildings where there is no venting provided for that plumbing fixture.
S-traps easily lose the water from the plumbing trap, especially if the S-trapped fixture is near a toilet or other large plumbing fixture.Cs sketch at left shows several types of illegal plumbing traps including the "S" trap.
When the larger fixture is draining, the sudden and large volume of water rushing down the drain creates a vacuum in the drain line that can siphon water out of the nearby plumbing traps.
When a plumbing trap has lost its water seal, sewer gases pass readily back into the building.
Look below the sinks for antiquated or un-vented drains - if you see an "S" trap rather than a modern "P" shaped plumbing drain trap, the fixture is almost certainly not properly vented.
Garbage Disposers (food grinders) and Plumbing Traps / Interceptors
Don't forget to check for smells at your garbage disposer drain too. And in buildings where a grease trap or grease interceptor is installed, the garbage disposer (food grinder) drainage is required to bypass the grease trap. This requirement is notwithstanding that garbage disposers (and the pre-rinse function of some dishwashers) is a substantial source of fats, oils, grease (FOG) that clog plumbing drain systems.
If that is the odor source you may be able to remove the odor by cleaning liquids or even simple vinegar.
Dry Plumbing Traps / Interceptors
Definition of Dry Plumbing Traps: a dry trap is a plumbing trap or interceptor that has lost its water seal, thus permitting sewer gases to escape back up building drain piping and out into the building through the fixture - an unsafe, unsanitary, and potentially dangerous condition.
When a plumbing trap remains un-used for a long time the water can simply evaporate from the trap, permitting sewer gases to back up into the building.
Watch out: Because sewer gas contains methane gas (CH4) there is a risk of an explosion hazard or even fatal asphyxiation.
Some places where we often find dry plumbing traps include:
There are various ways to deal with dry plumbing traps to stop smelly and dangerous sewer gas backups into the building.
Carson Dunlop's sketch at left shows how a trap primer system can be installed from a laundry tub. Other owners simply pour some mineral oil into unused traps.
Self-Sealing Traps for Floor Drains
Self-sealing plumbing traps (interceptors) containing check valves are available and are suited for floor drains. If water on the floor needs to escape it can flow out of the trapped floor drain, but the trap contains a mechanical seal which prevents sewer gas backups even if the floor drain trap is dry.
Clogged Plumbing Traps / Interceptors
Clogged or blocked plumbing traps can cause leakage, and organic debris in plumbing traps may itself be a source of odors which people mistake for sewer gas backups.
If your drains are slow at only certain fixtures one of the first things to check is for clogging of the individual fixture traps.
As Carson Dunlop's sketch shows, some fixtures such as laundry sinks are required to have traps which include a cleanout plug, making cleaning of the trap easier.
Otherwise you'll have to remove the entire plumbing trap to clean it. (Remember to put a bucket under a trap before trying to remove it, and remember not to try working on plumbing traps on Sunday night when you can't dash out to the building supply store to replace parts you've broken.)
Check your toilets for leaks at the toilet base. The wax ring used to seal the toilet base to the waste pipe at the floor may
be deteriorated or leaky, especially if the toilet is loose or was previously loose.
How to check for a loose toilet: Straddle the toilet and gently pinch it between your knees. Then gently push on each side of the toilet to see if it moves.
If the toilet moves it may be leaking into the floor (and ceiling below) - an unsanitary condition. The toilet needs to be removed, any damaged floor repaired, and then the toilet is reinstalled using a new wax toilet sealing ring before bolting it securely to the floor.
We provide a detailed list of sewer and sulphur gas odor sources at Sources of Sulphur Odors in buildings.
At PLUMBING DRAIN NOISES we explain the basics of proper plumbing vent piping and how errors cause trap siphonage, odors, and noises
Green link shows where you are in this article series.
Frequently Asked Questions (FAQs) about plumbing drain traps & traps on plumbing fixtures, sinks, tubs, showers, etc.
Question: can a dried out floor drain trap cause a sewage backup?
Can a dried out floor drain trap cause a sewer line backup? - Daryl 12/27/12
Reply: directly, no, indirectly ... maybe
Can a dry trap cause a sewer line backup?
No Daryl, a dried out floor drain trap doesn't cause a sewer line backup, at least not directly;
Questions & answers or comments about plumbing traps or plumbing interceptors
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Technical Reviewers & References
Related Topics, found near the top of this page suggest articles closely related to this one.