House Smells Like Sewer When It Rains? Do This

If there is a sewer smell in your house after it has rained, it is a sign that sewer gases are leaking from the plumbing system and accessing your home which should not be the case.

But why is there a sewage smell in the house specifically when it rains? Why not during any other time?


A sewer smell in the house when it rains is caused by cracked sewer pipes or septic tank, dried up drain traps, bad toilet wax rings or clogged plumbing vent. Rain also causes the air to be heavy, preventing sewer gases from flowing out but instead remain low to the ground and hence the sewage smell.

When it rains, there is a change in the atmospheric pressure which causes air surrounding your house to be heavy. This restricts sewer gases from flowing away from your house through the vent but instead saturate the air low on the ground and hence the sewer smell in the house.

Some people will also notice that there will be a sewer smell in the house during the night but the same will disappear during the day. Why is that the case?

The reason your house smells like sewer during the night is because the temperature is low, meaning the air is heavy and hence sewer gases are unable to flow away from the house. Instead they remain low on the ground saturating the air around it.

During the day when it is warmer, the air surrounding your house is lighter and hence the sewer gases can flow away easily.

For some people, the sewer smell is more concentrated in the basement when it rains. This is because the basement floor drain is the drain at the lowest level and when there is a problem with the sewer line it will be the first one to be affected.

To get rid and prevent sewer gases from the house when it rains, make sure that all drain traps are full of water, the plumbing vent is clear, there are no wobbling toilets and that you have no clogged drains. If you suspect a cracked sewer line or septic tank is the problem, have it inspected by a licensed plumber.

Let us now look at why you have a sewer smell in the house when it rains in more details, and what you can do to fix the problem.


If your house smells like sewer after raining, you may be able to solve the problem on your own if you are lucky. If however the problem is caused by a cracked sewer line or septic tank, you will need to work with a professional plumber.

The following are the different methods to get rid of sewer gas smell in the house after it rains:

1. Check the Drain Traps

Drains traps which are also known as P-traps or water traps are U-shaped bends on fixture drain lines. You can see them under your kitchen or bathroom sink as well as the toilet bowl but the ones in the shower, tub or washing machine drains are not visible.

All fixtures in your house that are connected to the sewer line have a P-trap. If you have a basement, you will have a floor drain which also has a P-trap though you cannot see it.

The function of the P-trap is to hold water at all times thanks to its shape. That is why you will always have water at the bottom of the toilet bowl.

The water in the P-trap acts a s a barrier preventing sewer gases from coming up through the drains, but to instead flow out through the plumbing vent.

If you have a fixture in your house that has not been used for a long time (like the guest bathroom toilet or sink), the water in the P-trap could have evaporated and broken the sewer gases barrier.

When that happens, sewer gases will flow through the drain and into your house without any restriction.

Apart from fixtures, if you have not used your basement floor drain for some time that could also be the problem.

The solution for this problem is usually a very easy one. Open all the fixture faucets in your house for about a minute and flush all toilets. Don’t forget to pour about a gallon of water down the basement floor drain.

The water will replace the evaporated water from the P-trap creating a new barrier. When you do that, sewer gases will now only flow out through the plumbing vent.

The reason the sewer gases smell is noticeable when it rains than when it is not raining is due to what I said earlier about rain changing the atmospheric pressure. 

With the air outside so dense, sewer gases will occupy the low levels of the vent and if there is an empty P-trap then the sewer gases will be forced out through it.

2. Inspect Sewer Cleanout Plugs

Sewer lines are designed in such a way that there is another pipe connected to them called cleanouts. Sewer cleanouts provide a way to access the sewer line in case the line needs to be inspected on cleaned.

A cleanout can be located outside the house but some people have them inside the house in the basement. The cleanout is found inside the floor drain on the side.

It is usually covered using a plug to prevent sewer gases from coming out. If the plug is missing, loose or broken then it means that sewer gases will flow out unrestricted through it.

Start by removing the floor drain grate and inspect the sewer cleanout. If the plug is missing or broken, you can always replace it for cheap.

3. Bad Toilet Wax Ring

Do you have a wobbling toilet in your house? When a toilet starts to rock about, it breaks the wax ring seal at the bottom of the toilet allowing sewer gases to leak out through it.

If that is the case, you will need to replace the wax ring. A wax ring cannot be reused.

The good thing is that a wax ring is cheap and also not that hard to replace.

Start by turning off water to the toilet then flush the toilet to remove water from the tank. Use a sponge to remove the water still left in the tank and the bowl.

Disconnect the water supply line to the toilet then use a wrench to loosen the nuts on both side of the bowl. Rock the toilet about to completely break off the wax seal then lift it off.

Use a putty knife to scrape off old wax from the bottom of the toilet as well as the top of the closet flange then place the new wax ring on top of the flange.

Set the toilet on top of the wax ring gently and tighten the nuts. Connect the water back to the toilet and flush it several times to make sure that the new seal is not leaking.

4. Cracked Sewer Line or Septic Tank


Cracked sewer lines could be the reason you are having a sewer smell in the house every time it rains. Surface/storm runoff will percolate through the ground and occupy the lowest point.

If you have a crack in one of your pipes, the water will enter the sewer line through it and displace the sewer gases inside forcing them out through the drains or the cracks.

The same could also happen to a septic tank. A crack on the septic tank will result in rain water filling it up and pushing out sewer gases back to your house. The smell will be even stronger if there is an empty P-trap somewhere in your house

Tree roots are the ones most responsible for cracks in sewer lines and septic tanks. This is unless you have a plastic sewer lines and septic tank.

The thing with a cracked sewer line or septic tank is that it is not a problem you can troubleshoot on your own. You will need to hire a professional plumber to do it.

A plumber will run a sewer inspection camera through the sewer line and they will be able to see the condition of the sewer line. They also have other specialized equipment that they use to hunt down leaks.

Hiring a plumber is not cheap but sometimes it is the only way to fix a problem.

5. Clogged Plumbing Vent

A plumbing vent is a vertical pipe connected to the house’s main drain line and runs through the roof of the house. It is responsible for removing sewer gases from the drainage system and also introduces in air for faster drainage.

If your vent stack is clogged, sewer gases will be trapped inside the drains lines and will force their way into the house through fixtures like toilets and sinks

Signs of a clogged plumbing vent .include:

  • Bathtub/shower drain gurgling when the toilet is flushed.
  • A toilet bubbling when flushed
  • Sink gurgling when the toilet is flushed or when the shower drains.
  • Toilet bubbling when the shower drains

To unclog a vent stack you will need to climb to the roof of the house armed with a garden hose or drain snake and probe it until the clog is out. I have written a detailed article on the same. Read it here.

Wrap Up

And basically that is why there is a sewer smell in your house when it rains as well as how to get rid of the smell. I hope this guide was helpful

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