Why Does My Septic Tank Smell When It Rains?

Imagine it's raining cats and dogs outside, and you’re indoors, cozy and carefree. Then it hits you — a whiff of something awful, like sewage. Hopefully, you haven’t had this experience and never will. But what if you become one of those whose homes smell unpleasant when it rains?

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The source of the stench is often sewer gas emanating from a faulty septic system. Luckily, there’s something you can do about it.

Why Does My Septic Tank Smell Like Sewage When It Rains?

Understanding the causes of why your septic tank smells when it rains is the first step to finding the solution and returning your home to its normal, comforting scent. Here are the five most common reasons:

1. Rainwater and Saturated Soil

If there’s been heavy rain, it can saturate the soil around your septic tank and drain field. This makes it difficult for the system to function like it should because the wet ground prevents the tank from properly processing and filtering waste. A sewage backflow is often the result.

2. Increased Pressure and Gas Release

One of the effects of heavy rain is atmospheric pressure changes. These fluctuations in pressure can force gases within your septic tank upward, channeling them through the plumbing system and eventually entering your home through drains and fixtures.

3. Dried-Out Water Barrier

Your plumbing system has P-traps, which are U-shaped pipes that hold water to block sewer gases from escaping into your home. If, for some reason, such as evaporation, there's no water, it opens a pathway for noxious gases to appear whenever it rains. This scenario is most likely to occur if the fixture, such as a sink or floor drain, hasn’t been used for a while.

4. Cracked or Broken Pipes

Cracked or broken pipes have gaps in the material, allowing space for rainwater to enter and subsequently expel sewer gases into your home. The most susceptible points in your home are the lowest ones, such as the basement or a ground-level bathroom.

5. Clogged Drains

A clogged drain traps sewage and wastewater, creating a toxic environment that’s waiting for the next batch of heavy rain. When it comes, the rain carries the smell through the plumbing system. It looks for the path of least resistance, which often means emerging inside your home.

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How to Get Rid of the Sewer Smell

There are several steps you can take to tackle the problem effectively. Let’s look at each step in sequence.

1. Check for Dry Traps

The first thing to do is check all the P-traps in your home, especially those that are rarely used. Pour a small amount of water into the drain, as this will either top up the water already sitting in the P-trap or fill it up if it’s empty. If your home is particularly prone to P-traps drying up, it’s worth making this task a routine.

2. Inspect Your Septic System

Although DIY has many benefits — chief among them a sense of personal satisfaction — nothing compares to the peace of mind that comes with hiring a professional. They bring their expertise to the task of checking for any damage to your tank or pipes. They make sure your system functions correctly and recommend necessary repairs, which could save you money in the long term.

3. Improve Drainage Around Your Septic System

The area around your septic tank and drain field must be well-drained to ensure it isn’t saturated during heavy rain. You might need to adjust the landscape or install drainage solutions to redirect water away from the septic system. This could be a DIY job if you’re confident in your abilities. If not, it’s best to call in a professional.

4. Address Clogged Drains and Toilets

If clogged drains are the reason foul odors enter your home, consider using a drain cleaner. There are manual versions (often called "drain snakes") and chemical alternatives. (Note: If using this method, strictly follow the manufacturer’s safety instructions.) If you’re not sure it’s the drains, call a plumber to inspect them and clear any blockages

5. Seal Cracks and Leaks

Check the plumbing system in your home for cracks and leaks, and seal any you find, no matter how small they appear to be. Sealing visible cracks and repairing broken pipes is a very effective way of reducing the chance of sewer gas entering your home.

6. Ventilation Improvements

The previous steps deal with repairs and maintenance, but what can you do while the smell is in your home? The answer is exhaust fans. Position them in the rooms where the odors are worst and move them around when necessary.