Sewer gas is a mixture of inorganic gases created by the action of anaerobic (needing no oxygen) bacteria on sewage and sludge. This gas can contain hydrogen sulfide, ammonia, carbon dioxide, methane, nitrogen, and hydrogen. Smelly and potentially explosive sewer gases are lighter than air and will rise up through plumbing drain or sewer systems unless these gases are blocked from entering the building.
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Plumbing drainage systems are designed to keep this sewer gas inside the pipes and any that does exit to the atmosphere happens outside the home through the vent pipes that poke up through the roofs of houses.
What causes sewer gases?
The source of the sewer gas can be plumbing fixtures whose traps have gone dry or have lost enough water that the water seal within the trap has broken. You would be surprised to discover that water can rapidly evaporate from toilets and the traps below tubs, floor drains and just about any fixture within a few months.
Cracks in either plumbing drain lines or vents pipes are the other source of sewer gas leaks. If the crack is in a drain line, you often see an associated water leak. But vent pipe cracks are far more elusive. They can leak vast amounts of sewer gas and you might not be able to locate the source easily without a special machine.
Sewer gas problems can also be caused by plumbing vent pipes that are clogged.When a vent pipe is clogged, the replacement air needed by the system will get sucked into the pipes through a fixture inside the house. When a large amount of water is placed into the drain pipes by a toilet or a powerful washing machine pump, it can readily suck the water out of a nearby bath tub trap or even a kitchen sink trap. Once this happens, sewer gas immediately enters the room through the dry fixture trap.
A damaged drain line. If the drain line is cracked or broken between the main sewer and the trap, there is nothing to impede the flow of gases through the crack or break in the line. Also, a damaged drain line may allow sewage to drain into the basement or crawlspace under your house, and you may get a sewer odour from that accumulation of sewer.
What should you do to avoid sewer gas or suspect sewer gas?
Locate the source of the odour. If it's coming from a toilet, the toilet may need servicing. If you smell the odours at a fixture drain, the vents are probably blocked. Smells coming from the wall signify the need to repair cracked or disconnected vent pipes.
Pull off the toilet if the smells originate there. Do this by turning off the water, draining the tank and unscrewing the toilet bolts with a wrench. Examine the subfloor for moisture damage. If you see any, repair the damaged sections.
Raise the flange if the top is more than 1/2 inch below the surface of the flooring. When the flange is too low, the wax ring can't seal the waste line, and sewer gases can pass through it. Unscrew the flange with a screwdriver, place a flange extender on top of it, and replace the screws to hold the flange and extender to the subfloor. Replace the toilet when you're done.
Clear the vents if the odours originate from a fixture P-trap. You are able to smell the gases at that fixture because the trap has been emptied by a vacuum in the waste line. Confirm this by pouring water down the sink to fill the trap and then flushing the nearest toilet. You'll probably hear sucking and gurgling sounds coming from the fixture.
Climb on the roof with an extension ladder and clear debris from the vent opening. The vent is usually situated just above the main bathroom. It may be blocked by leaves, sticks or even a dead bird.
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Insert a sewer auger into the vent and push it down as far as you can if the water overflows. Crank the handle to work the auger through the blockage. When the blockage has been cleared, the water standing in the vent pipe will drain. Spray more water to make sure the vent is open.You can also examine the vent pipes in the wall if the smell originates from there.
Re-glue loose joints in the vent pipes with plastic pipe cement. Because vent pipes don't carry water, plumbers often forget to glue them, and odors can seep from unglued joints. Repair cracked or failing fittings by cutting them out with a hacksaw and gluing in replacement pipes and fittings.
QUICK TIP
To slow evaporation from fixture traps that are not used on a frequent basis, fill them with water and then slowly pour about 100 grams of mineral oil into the fixture or floor drain. This mineral oil will evaporate far more slowly than water and the trap will remain wet for many months.
