A smelly kitchen sink is caused by decomposing food waste in the drain line, empty P-trap, a clogged plumbing vent or a dirty garbage disposal. An S-trap instead of a P-trap could also be the reason your kitchen sink has a horrible smell.
To get rid of the smell from your kitchen sink, clean the drain line using baking soda, vinegar and hot water. Also, make sure that the P-trap is full of water and that the plumbing vent is not clogged. If you have an S-trap, replace it with a P-trap or install an air admittance valve.
A sewer smell from the kitchen sink is a sign that the P-trap is empty or the plumbing vent is clogged. If you have an S-trap instead of a P-trap, the water in the trap will always be siphoned out when the sink is draining allowing sewer gases to come out through the sink drain.
If the smell from the kitchen sink comes and goes, you most likely have a problem with the drain trap. When there is water in the trap, there will be no smell. However, when there is no water in trap, sewer gases come up through the sink drain. You could as well be having an S-trap.
If your kitchen sink smells like rotten eggs or sulfur, it is a sign that you have rotting waste or a biofilm in the drain line. This is due to accumulation of food waste in the drain line and P-trap resulting in the formation of hydrogen sulfide gas which smells like rotten eggs.
If your kitchen sink smells like a dead animal, there is rotting food waste, grease and other forms of waste in the drain line, P-trap and garbage disposal. Cleaning the sink using baking soda, vinegar and boiling water will get rid of the smell.
A kitchen sink that smells like ammonia means that sewer gases are getting back to the sink drain line instead of exiting through the plumbing vent. That is usually caused by an empty P-trap, or when you have an S-trap instead of a P-trap.
Why Kitchen Sinks Smell?
Let us now look at the reasons why your kitchen sink is smelling in more details. The following are the causes of a smelly kitchen sink:
1. Rotting Food Waste in the Drain Line
Unlike a bathroom sink, there is a lot of solid waste that goes down the kitchen sink day in day out. Most if not all of that waste is usually organic in nature.
The one thing we know about organic substances is that they decompose easily. The rotting/decomposition is caused by bacteria with emission of a horrible odor. That could be the reason you are having a nasty smell in your kitchen sink.
The U-bend (P-trap) under your kitchen sink causes some resistance when solids are being drained out from the sink. As such, it is very easy to have food waste accumulate inside it and start to rot.
If you have a slow draining kitchen sink and that is smelling at the same time, you most likely have gunk inside the P-trap that is restricting flow of water and also causing the bad smell.
Kitchen sink smell associated with rotting food waste in the drain line can be identified as a smell similar to that of rotten eggs or a dead animal.
If you therefore have a dead animal smell coming from your sink don’t think that there is a dead animal carcass trapped in the drains. It is food waste in the drain line decomposing.
A sticky film can also develop inside the kitchen sink drain and cause a bad odor. The slimy substance is called a biofilm, and is formed when bacteria come together and starts to multiply.
Not only is the biofilm responsible for drain smells but it could also make you sick. Although rare, some of the illnesses associated with biofilm are Salmonella, E. coli, and Legionnaire’s disease.
2. Dirty Garbage Disposal
If you have a garbage disposal connected to your kitchen sink, there is a very high likelihood of having a smelly kitchen sink.
Garbage disposal shred food scraps using blades and then force the slurry out through the kitchen sink drain line. That is why it is critical to run the garbage disposal while running water at the same time.
The water is spun around the garbage disposal where it cleans out all the grinded waste and flushes it out of the unit. The main reason why garbage disposals smell is because folks don’t run them with enough water. More on smelly garbage disposals in this post.
If you have a double-bowl kitchen sink where the garbage disposal is connected to one sink bowl, a tee pipe will be used to connect the 2 bowls to the same drain line.
It is very easy for waste to accumulate inside the tee, especially if you don’t use enough water. After a short while, the food waste will start to decompose followed by a horrible smell.
A lot of folks also forget to clean the garbage disposal splash guard. You will be surprised by the amount of waste trapped underneath the splash guard which needless to say will cause a nasty odor after just a few days.
3. Empty P-trap
In case you have been wondering, the U-shaped pipe under your kitchen sink is called a P-trap. It is also called a drain trap, U-bend or even U-trap.
All the fixtures in your houses connected to the drainage system like bathroom sink, shower, toilet, bathtub and washing machine drains all have P-traps.
A P-trap has 2 main functions:
- It traps solids which would have otherwise clogged the drain line farther away where unclogging would be more difficult.
- Thanks to its shape, it holds water at all times. The water acts as a barrier preventing sewer gases from coming up into the kitchen or bathroom.
If you therefore have a sewer smell coming from your kitchen sink, it is clear that your P-trap is either not properly installed or it is empty.
One of the reasons a P-trap could be empty is when it has not been used for a long time. If for instance you have just come back from a vacation and noticed a sewer smell coming from your kitchen sink, the water in the trap could have evaporated.
Evaporation of water from the P-trap means sewer gases will enter the kitchen without any restriction.
Another reason your P-trap could be empty could be that it is leaking. Check underneath the kitchen sink if you can see water dripping from the P-trap or if there is standing water on the cabinet floor.
4. Clogged Plumbing Vent
A plumbing vent is the vertical pipe which runs through the roof of your house. It is usually connected to the waste/soil stack where all the other drain lines are also connected to.
A plumbing vent has 2 main functions:
- It introduces air into the drainage system. This allows fixtures to drain fast and toilets to flush better.
- It allows sewer gases to exit the drainage system.
What then happens when a plumbing vent is clogged?
- Sewer gases cannot exit the drain lines
- Air cannot be introduced into the drainage system and hence the creation of negative air pressure.
When there is a buildup of sewer gases in the drain lines, there will be nowhere for them to go other than force themselves out through the P-trap despite it being full of water.
If you are keen enough you can hear the P-trap bubbling. In the case of a toilet you will see the bubbles on the water at the bottom of the bowl.
Another thing that can happen when the plumbing vent is clogged is that the water in the P-trap could be siphoned out. How does that happen though?
If say you have a clogged plumbing vent and you drain a washing machine, bathtub or flush a toilet, the water will create negative air pressure (vacuum) as it drains. This is because the vent is clogged and air cannot get in to the system.
The vacuum created will suck the water from the kitchen sink P-trap and when that happens, you will have sewer gases coming out of the sink. This will continue until you use the sink since that will restore the water in the trap.
So, how do you know that you have a clogged plumbing vent? It is actually very easy.
Since all the fixtures are served by the same vent, a clogged vent will affect all the fixtures. The following are some of the telltale signs of a clogged plumbing vent:
- Sewer smell in the bathroom
- Gurgling drains
- Toilet bubbles when flushed
- Slow draining fixtures
- Weak flushing toilet
Ream more about the telltale signs of a clogged vent in this post.
5. You Have an S-trap
Does your kitchen sink have an S-trap or a P-trap? Do you even know the difference between the two traps?
If you live in a relatively new house or one that has been remodeled then you most likely have a P-trap. However, sink drains in old houses could still be having S-traps.
As a matter of fact, S-traps are illegal for the reason I outlined in this post. No plumber will install an S-trap for you since it will be in contravention of the code.
The main difference between a P-trap and an S-trap is that a P-trap is formed by a single U-shaped pipe which resembles an inverted P while and S-trap is formed by 2 U-bends and hence it looks like an S.
Also, the U-bend in a P-trap is connected to a horizontal drain line while the S-trap is connected to a vertical drain line. But why is that important?
You see, when draining a sink with a P-trap, air can still get back to the trap thanks to the horizontal drain line. On the other hand, the vertical drain line connected to the S-trap will not allow air to get back to the trap.
The effect of this is that negative air pressure is created in the drain line which sucks water from the S-trap leaving it empty. With an empty trap, sewer gases will flow freely to the kitchen sink.
If you can hear your kitchen sink gurgling when it drains, you could very well be having an S-trap. The gurgling is as a result of the water in the trap being siphoned out.
How to Remove Smells from a Kitchen Sink
The good thing is that getting rid of that terrible smell from your kitchen sink is not that hard. Most people will do it without the need to call in a plumber.
The following are some of the ways to get rid of smells from a kitchen sink:
1. Clean the Sink Using Baking Soda, Vinegar and Boiling Water
Baking soda is an alkali while vinegar is a weak acid. When combined together, the 2 react in a fizzing reaction which is what breaks down the gunk inside the P-trap and drain line.
Boiling water on the other side will help to further melt and dissolve the gunk and biofilm thereby leaving the sink smelling fresh. Here is how to do it:
- Pour 1 cup of baking soda down the drain.
- Slowly add 1 cup of vinegar.
- Give the solution about 15 minutes to work out its magic.
- As you wait, boil about 1 gallon or more of water.
- Dump the boiling water down the drain
In most of the cases this easy method will completely remove the smell from your kitchen sink.
2. Clean the Garbage Disposal
If you kitchen sink is connected to a garbage disposal, you have to clean the garbage disposal as well. The first step will be to clean it using baking soda, vinegar and boiling water as I have outlined above.
After that, you need to scrape the inside of the garbage disposal. And how do you do that?
- Fill up the garbage disposal with ice cubes.
- Squirt about a ¼ cup of dish soap into the disposal
- Start the garbage disposal and run it with cold water until all the ice cubes are finished.
As the ice cubes are spun around the inside the garbage disposal, they will scrape the walls of the disposal removing all food scraps with the help of the dish soap. The ice cubes are also very effective in sharpening the garbage disposal blades.
To clean the garbage disposal splash guard, use a special garbage disposal brush which you simply push down and all the way up until you have removed all the gunk hiding underneath it.
To keep the garbage disposal smelling fresh, throw some lemon wedges inside it one at a time and run it with a trickle of cold water.
3. Fix the Empty P-trap
If the P-trap is empty because you haven’t used the kitchen sink for a while, all you need to do is turn on the faucet for a few seconds to replace the water that has already evaporated. That should be enough to fix the problem.
If on the other hand you have a leaking P-trap, try to tighten the connections and see if that fixes the problem. Replace the P-trap or call a plumber to do it for you if you the leaking persist.
4. Unclog the Plumbing Vent
If you have established that you are dealing with a clogged plumbing vent, you can either unclog it yourself or call a plumber to do it for you.
This is how to unclog a plumbing vent:
- Grab the garden hose and climb with it to the roof of the house.
- Locate the vent stack.
- See if you can remove clogs from the top of the vent with your bare hand.
- Stick the hose inside the plumbing vent and use it to try and loosen the clog.
- Have someone on the ground also turn on water to the hose. The weight of the water inside the vent could be enough to clear the clog.
- If the clog just won’t budge, use a plumber’s snake to clear it or contact a professional plumber.
5. Replace the S-trap
If you have an S-trap, there 2 things you can do; learn how to live with it or replace it with a P-trap.
If you choose to live with the S-trap, make sure you pour a little water down the drain after draining the sink. That should replace the water siphoned from the trap.
Most DIYers cannot replace an S-trap with a P-trap. Majority of those who try only end up with 2 S-traps in series. I would highly recommend hiring a plumber to do it for you.
Alternatively, you can install an air admittance valve under the kitchen sink. What the air admittance valve does is introduce air into the S-trap as it drains therefore preventing the formation of negative air pressure.
And basically that is how to remove the smell from your kitchen sink. I hope you found this post useful.