Laundry Room Sewer Gas: Causes And Solutions

Sewer gas in your laundry room is not only unpleasant but can also be dangerous for your health. The smell resembles rotten eggs due to the presence of hydrogen sulfide in the gas. If you notice a sewer gas smell in your laundry room, it is important to address it immediately.

There are several possible causes of sewer gas smell in the laundry room, including dry water traps, a missing clean-out cap or plug, a bad wax ring on the toilet, or a sewer or septic pipe leak. Water traps, sometimes called P-traps or S-traps, are commonly located near floor drains and laundry tubs, and they work by trapping water inside the curve to block gas from entering the house. If the water in the trap dries out, it can allow sewer gas to leak into the room. This can be fixed by simply pouring water into the drain to restore the trap.

Another possible cause of sewer gas smell is a missing clean-out cap or plug. Clean-out plugs are access points in the main sewer lines, usually at the foundation walls, and they prevent gases from the clean-out line from entering the house. If the cap or plug is missing or broken, it can be replaced with a new one from a hardware store.

A bad wax ring on the toilet can also cause sewer gas smell. The wax ring provides a watertight and airtight seal between the toilet flange and the base of the toilet, and if it leaks or becomes compromised, it can allow sewer gas into the home. In this case, the wax ring will need to be replaced.

More serious repairs may be required if the cause of the sewer gas smell is a sewer or septic pipe leak. This is usually indicated by gurgling toilets and slow drains, in addition to the sewer gas odor. Loose connections along the vent pipe or sewer line can allow pungent gases to enter the home, and an experienced plumber will be needed to correct this issue.

Dry water traps

If you suspect that your P-trap is dry, you can try pouring a few cups of water into it to restore the water seal. However, this solution is often short-lived, as the water will likely evaporate again within a few days. A more effective solution is to use a trap seal primer, which automatically provides a supply of water to the P-trap when a sink is used or a toilet is flushed.

If you are experiencing sewer gas odours in your laundry room, it is important to act quickly, as prolonged exposure to sewer gas can be hazardous to your health. Sewer gas contains methane, which is highly flammable and can cause symptoms such as weakness, headaches, dizziness, nausea, and even suffocation.

Sewer or septic pipe leaks

• Tree roots: Tree roots can invade sewer pipes through seams, joints, or small cracks, leading to blockages and leaks.
• Clogged sewer pipes: Recurring clogs can lead to leaks as the water finds alternative escape routes, causing cracks or breaks in the pipes.
• Old age: Older homes with cast iron pipes may experience pipe deterioration and failure over time due to cracks, root intrusion, or misaligned connections.
• Improper installation: Newly installed appliances, such as washing machines, may be incorrectly attached to the drain line, allowing gas from the sewer to enter the home.
• Broken or cracked pipes: Damage to sewer pipes can occur due to various reasons, including tree root intrusion, extreme weather events like floods, or pipe corrosion.
• Blockages: Sanitary sewer backups usually occur at the lowest open drain due to blockages in the line. Regular backups may indicate underlying issues such as root intrusion, cracks, or misaligned connections.
• Foundation issues: In severe cases, leaks from broken sewer pipes can lead to foundation problems, including cracks, settlement, and even sinkholes.
• Insect and rodent infestations: Cockroaches, sewer flies, and rats can enter homes through cracks in sewer pipes, posing health risks and requiring immediate attention.
• Mold growth: A cracked sewer pipe can increase humidity levels, creating favourable conditions for mold growth, which can further deteriorate the pipes and pose health hazards.

Improperly installed washing machine

If you've recently had a new washing machine installed, it could be the cause of the sewer gas smell in your laundry room. Installers sometimes make the mistake of attaching the machine to the drain line without anything to block the gas from the sewer. If this is the case, you'll need to get the machine reinstalled and the drain line sealed.

The wastewater from a washing machine flows through a flexible hose into the drain box pipe, which connects to the P-trap. The P-trap is a U-shaped pipe designed to trap and hold water, creating a barrier that blocks sewer gases from escaping through the drain. However, because the hose connecting the washing machine to the P-trap is flexible, it can be inserted too far into the drainage box, preventing the P-trap from functioning properly. As a result, sewer gases can seep into your laundry room.

To solve this problem, try pulling the washing machine drain hose out of the drain box. Stop when the hose is roughly eight inches deep in the piping—this will allow the P-trap to work correctly and prevent sewer gases from leaking into the room.

Clogged vent pipe

A clogged vent pipe can cause sewer gas to back up into your laundry room, resulting in an unpleasant and persistent sewer smell. This can be caused by debris, leaves, or nests from birds or rodents blocking the vent. A clogged vent pipe can also lead to gurgling or bubbling sounds from your drain pipes and slow drainage in your sinks, bathtubs, and toilets.

If you suspect a clogged vent pipe, there are several steps you can take to address the issue:

• Visual Inspection: Begin by inspecting the vent pipe on your roof for any visible obstructions, such as debris, leaves, or nests. Ensure that the vent cap is intact and not obstructed.
• Use a Vent Snake or Auger: If you suspect a blockage within the vent pipe, you can use a vent snake or auger to dislodge obstructions and clear the vent. Insert the snake carefully into the vent and rotate it while applying gentle pressure.
• Flushing with Water: Another method is to flush the vent pipe with water by carefully pouring a bucket of water down the vent stack. This can help push any debris or blockages down the pipe and clear the vent.
• Professional Assistance: If your attempts to clear the vent pipe are unsuccessful or if you're uncomfortable working at heights, it's advisable to seek professional plumbing assistance. Plumbers have specialized equipment and expertise to safely and effectively address venting issues.
• Preventative Measures: To avoid future clogs and sewer smells from vent pipes, consider installing a vent cap or screen to keep debris, leaves, and critters out of the vent stack. Regular maintenance of your roof and gutters can also prevent debris accumulation around the vent.

It's important to note that sewer gas can be dangerous, so if you're unable to locate the source of the smell or resolve the issue, it's best to contact a professional plumber for assistance.

Sewer gas backing into the house

Dry Traps

One of the most common causes of sewer gas backing up into the house is dried-out water traps, also known as P-traps or S-traps. These traps are designed to hold water and prevent gas from returning to the house. However, if the water evaporates, the trap becomes ineffective, allowing gas to leak into the house. This is often the case with floor drains, laundry tubs, and sinks that are not used frequently. To fix this issue, simply run some water or pour a pitcher of water down the drain to restore the water trap. You can also add a couple of tablespoons of cooking oil or vegetable oil to the water to create a floating seal that slows down evaporation.

Missing Clean-Out Caps or Plugs

Clean-out plugs are access points in the main sewer lines, usually located at the foundation walls. They are used for snaking out the line and removing clogs. The caps or plugs on these clean-out lines can sometimes fall out, break, or go missing, allowing gases to enter the house. If you notice that the cap or plug is missing or damaged, you can purchase a replacement plug at any hardware store.

Faulty Wax Ring on the Toilet

Between the toilet flange and the base of the toilet, there should be a wax ring that creates a watertight and airtight seal. Over time, this wax ring can leak or become compromised, allowing sewer gas to escape into the home. If the wax ring is the source of the problem, it will need to be replaced.

Improperly Installed Washing Machine

If you have recently installed a new washing machine, it could be the culprit of the sewer gas smell. Sometimes, installers attach the machine to the drain line without properly sealing it, allowing gas from the sewer to enter the laundry room. In this case, you will need to have the machine reinstalled with a proper seal on the drain line.

Sewer or Septic Pipe Leaks

Sewer and septic line leaks are more challenging to diagnose and typically require an expert to repair. If you suspect a leak, look for signs of gurgling in your toilet, slow drains, or a persistent sewer gas odor. These leaks can be caused by loose connections along the vent pipe or sewer line, often inside a wall or ceiling, requiring the assistance of an experienced plumber.

Mildew or Bacteria in the Washing Machine

Sometimes, the sewer gas smell may not be caused by a leak at all but by the growth of bacteria, mold, or mildew in your washing machine. This can happen when soap, mildew, lint, mold, and built-up dirt accumulate in the crevices of the drum and rubber seal of the washer. To clean the washing machine, check if it has a self-cleaning cycle. If not, add a cup of bleach and run it on the longest cycle with hot water. If cleaning the machine does not eliminate the smell, it is best to consult a plumber to rule out a sewer leak.

Frequently asked questions