Sulfur smell in the house signifies the presence of hydrogen sulfide gas. It is formed when bacteria break down organic matter, usually in stagnant waters with low oxygen content. The gas also smells like rotten eggs.
A sulfur/rotten eggs smell from drains is a sign that the drain is clogged, allowing bacteria to break down waste and create hydrogen sulfide gas. It could also be caused by an empty P-trap or clogged plumbing vent and hence sewer gases come out through the drains.
If you have a slow draining fixture and also have a sulfur smell coming from the drain, there is a partial clog in your drain line or P-trap. Bacteria are therefore breaking down the clog material and in the process produce hydrogen sulfide gas.
To get rid of sulfur smell in your drain, clean the drain line and P-trap using baking soda, vinegar and boiling water. Also, clear a clogged plumbing vent, make sure P-traps are full of water and replace S-traps with P-traps.
It is important to know that all your drains are interconnected and drain out through one sewer line buried in your front yard. As such, it is not unusual for 2 or more fixture drains to “communicate”.
If your kitchen sink smells like rotten eggs when the washing machine is on, you most likely have a clogged plumbing vent. Since the sewer gases cannot exit through the vent, the water from the washing machine compresses them and forces them out through the sink drain.
If the sink smells like rotten eggs when the dishwasher is draining, it is a sign of rotting food waste in the drain hose or filter creating the hydrogen sulfide gas. It could also be caused by a clogged plumbing vent, which forces sewer gases out through the sink drain.
If you have a rotten eggs smells in your garbage disposal, pour 1 cup of baking soda followed by another cup of vinegar and after 15 minutes run it using hot water. To keep it smelling fresh, throw in lemon wedges one at a time and run it using cold water.
Let us now look at the reasons you have a sulfur smell coming from your drains in more details.
1. Empty P-trap
A P-trap is the U-shaped bend underneath your bathroom or kitchen sink. As a matter of fact, every drain in the house has a P-trap only that you cannot see the one in your shower, bathtub or washing machine drain.
A P-trap has two main functions:
- Due to its shape, it traps solid wastes which would have otherwise clogged the drain pipe farther away. It is usually easy to clean the P-trap than unclog the main drain line.
- Again thanks to its U-shape, the P-trap is always full of water. The water acts as a barrier preventing sewer gases from coming up through the drain. Instead, sewer gases should exit the drainage system through the plumbing vent.
If the P-trap is empty, sewer gases will find it easy to exit the system through the drain instead of traveling upwards through the plumbing vent. But why would a P-trap be empty?
One of the main reasons why a P-trap would be empty is when a particular drain has not been used for some time. This includes the bathtub or guest bathroom sink or shower.
If the fixture has not been used for a while, water will evaporate out of the P-trap leaving it empty. When that happens, sewer gases will flow out through the drain without any restriction.
Another reason the P-trap could be empty is if it is leaking. Check if there is a pool of water underneath your bathroom or kitchen sink.
A leaking P-trap will drain the water out of the trap leaving it empty. This is however rare unless you or someone in the house has tampered with the P-trap.
The other reason your P-trap could be empty is if you have a clogged plumbing vent. Let me address that in a separate heading.
2. Clogged Plumbing Vent
A plumbing vent is the vertical pipe which runs through the roof of your house. It has 2 main functions:
- It is responsible for removing sewer gases from the drainage system.
- It introduces air into the drainage system, allowing fixtures to drain faster and toilets to flush strongly.
If the plumbing vent is clogged, none of the above is going to happen. Instead, sewer gases will build up inside the drain pipes and there will be no way for air from outside to equalize the air pressure inside the drainpipes.
In this case what will happen is that if you for instance flush the toilet, negative air pressure will be created inside the drain line as the column of water drains out. This is because air from outside cannot flow in.
Negative air pressure (vacuum) is very unstable and will therefore try to pull air from the surrounding. The only problem will be the water in the P-traps.
In a bid to pull air from the surrounding, the water from the nearby P-traps (like shower or sink) will be siphoned out, leaving the P-trap empty.
If you hear your shower drain or bathroom sink gurgling after flushing the toilet then it is a sign that the vent stack is clogged. The gurgling sound is caused by the siphoning of water from the P-trap.
Other signs of a clogged plumbing vent include:
- Toilet bubbling when flushed
- Rotten eggs smell from sink when washer is draining
- Slow drains
- Weak flushing toilet
- Gurgling drains
3. Clogged Drains
A P-trap is without a doubt a great addition to the drain-waste-vent system but it also has one main disadvantage.
Due to its shape, solid waste has to go down then up inside the P-trap. As such, some of the waste ends up getting trapped there, resulting in a clog.
It does not even need to be a full clog. A partial clog is enough for you to have a sulfur gas smell coming from your drains.
As you already know, most of the waste that goes down our drains is organic in nature. We also know that organic waste is easily broken down by bacteria.
Bacteria will simply break down the waste inside the P-trap and in the process create hydrogen sulfide gas. Some people even claim to experience a smell similar to that of a dead animal.
4. You Have an S-Trap
Do you have an S-trap instead of a P-trap? And what is the difference between the 2 types of traps.
If you live in an old house, there is a big chance that you have an S-trap and not a P-trap unless the house has been remodeled.
The difference between a P-trap and S-trap is that a P-trap only has one U-bend and is connected to horizontal drain line. On the other hand, an S-trap consists of 2 U-bends connected to a vertical drain line.
With a P-trap, air is able to get back to the trap when the sink is draining, thanks to the horizontal drain line. When a fixture connected to an S-trap is draining, there is no way for air to get to the P-trap since the vertical drain line is full of water.
As such, negative air pressure will be created and the water inside the S-trap will be siphoned. With an empty drain trap, sewer gases will flow out through the drain until you run a little water through the sink. That is the reason why S-traps are illegal.
How Do You Get Rid of Sulfur Smells in Drains?
The following are the 4 main ways to get rid of the sulfur smell from your drain:
1. Fix the P-trap
With an empty P-trap, if the reason the P-trap is empty is because it hasn’t been used for a while, the only thing you need to do is pour a little water down the drain. That should replace the water that has evaporated.
And that is also the reason you should run some water through all your drains and flush your toilets every time you come back home from a long vacation. The water replenishes the evaporated water in the P-trap.
If you are dealing with a leaking P-trap, try to tighten the connections or replace it altogether. I have written a separate article on the same here.
2. Unclog the Plumbing Vent
If it looks like a clogged plumbing vent is the problem, unclogging it can be a very simple process. Here is how to unclog a plumbing vent:
- Climb to the roof of the house armed with a garden house and/or plumber’s snake.
- Locate the vent.
- Check if there are blockages at the top of the vent which you can easily remove with your bare hands.
- Stick the garden hose down the vent and use it to clear any clog you may experience.
- Have someone on the ground turn on water to the garden hose. The weight of the water can be enough to dislodge the clog.
- If the clog won’t just budge, upgrade to a plumber snake.
- Push the snake down the vent until you encounter resistance.
- Crank the snake handle until you move past the restriction. Keep pushing the snake down until you are certain there are no more clogs.
3. Clean the P-trap
Cleaning the Drain traps is a sure way of getting rid of the sulfur smell from drains. You should actually clean your drain traps frequently even when there are no smells just to keep them open and prevent smells in the first place.
Here is how to clean a P-trap:
- Pour 1 cup of baking soda down the drain.
- Slowly add another cup of vinegar.
- Wait for about 15 minutes for the solution to break down the gunk in the P-trap.
- Dump about a gallon or more of boiling water down the drain. The water will melt the clog further and flush it down the drain.
Another method of cleaning the P-trap is by removing and physically cleaning it. Just disconnect the connections under the sink and scrub it using a flexible wire brush.
If the smelly drain is your kitchen sink which is also connected to a garbage disposal, do not forget to clean the garbage disposal as well.
Apart from cleaning the garbage disposal with baking soda and vinegar, ice cubes dish soap and rock salt also works wonders.
Just fill the garbage disposal with ice cubes, add ¼ cup of rock salt and squirt a generous amount of dish soap. Run the garbage disposal with cold water until all the ice is over.
The ice and salt helps to scrape the walls of the garbage disposal thereby removing all the food scraps stuck there. You can afterwards throw lemon wedges one at a time inside the disposal and run it using cold water.
4. Replace S-traps with P-traps
If you have an S-trap in one of your drains, have a plumber come over and replace it with a P-trap. I would recommend a plumber doing this instead of a DIY.
Alternatively, you can install an air admittance valve under the sink. This is something you can do on your own.
And basically that is how to get rid of sulfur smell from your drains. I hope this guide was helpful.