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Toxic Sewer Gases and your Plumbing System

Typical Venting System for Residential Plumbing. Newer style shows use of Air Admittance Valves or AAVs rather than multiple roof penetrations.

What is sewer gas?

Sewer gas is a byproduct of the breakdown of natural human waste. It comprises a mixture of gases, including hydrogen sulfide, ammonia, and more. The hydrogen sulfide in sewer gas is what gives it its signature rotten egg smell.

Sewer gas isn’t necessarily toxic at low levels. However, chronic exposure, or higher levels of exposure, can cause symptoms of sewer gas poisoning.

We all take sewer gas (or lack of sewer gas) for granted. We use our kitchen sink, bathroom sinks and tubs, we flush our toilets but we don’t really think about why these drains don’t smell bad (unless there is a problem).

We will discuss the reasons sewer gases do not enter the inside air of our homes and businesses.



The P-trap keeps sewer gases out by keeping a small curve of piping full of water. This is called the trap seal

Toilet Seals/Wax Rings

Toilet leaking at base
A toilet leaking at base can indicate a compromised seal which can let out harmful sewer gases. If you smell foul odors in your bathroom it could mean an issue with the seal between your toilet and the flange.

Air Admittance Valves

Air Admittance Valve
An Air Admittance Valve or AAV allows fixture(s) to vent properly without the need of an additional roof vent.

Air Tight Drains

The drain waste and vent system is an important part of any dwelling, it allows for proper drainage and protects the health of inhabitants by keeping sewer gasses out of the building while properly evacuating human waste. Per Florida Plumbing Code 901.2, all plumbing vents must be air tight. The gases can escape through the required minimum 1 roof penetration vent. Healthy drain lines will be sealed to prevent any leaking substances or gases into the home or surrounding area.

I smell sewer gases in my home in Florida, what could it be?

Things to look for…

Check unused drains. Drains or toilets that go unused may have had their traps dry out. If the P-Trap or Toilet trap dried up it may not form a trap seal and allow gases to exit!

If you smell sewer gases in your home it can be harmful to your health. Start with the most common causes. 1 in 8 septic tanks in the USA is right here in Florida so it could be a full septic tank or a failing septic system is backing up into your home causing foul odors from the toilet or shower drains backing up. If you are on city sewer it could be a blockage in the line causing backups to wreak havoc on your nose!

If you are sure it is not a clogged line or a full or failing septic system check if the smell is stronger near a bathroom or kitchen.

If the smell is strongest near a bathroom check the toilet for leaks at the base, listen to the toilet flush if it sounds like air is getting in then sewer gases may be getting out!

If the smell is stronger under a kitchen or bathroom sink check your Air Admittance Valves if present. Their lifespan can range from 10 years to 20 years and if they are starting to fail it may be time to replace them. Remember Air Admittance Valves are mechanical and do need to be replaced over time as routine maintenance.

If your smell is persistent even after the basic checks above, make sure it is not related to contaminated water (this can happen on well water). If you are still unsure of the source of your foul odors in your home it may be time to call out the experts. At times special equipment may be necessary to hunt down your sewer gas leak. Equipment like a drain camera can identify drain problems and smoke machines can help pinpoint a venting leak.

Below is an example of root penetration found in Lake County, Florida. Here at Prime Plumbing, we can handle any drain problem residential or commercial. Feel free to call us 24/7/365. 352-357-3700.

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