One of my friends based in Scranton, PA had an older 1960s home with a renovated kitchen (Fun trivia: most cities with the oldest homes are in the Northeastern U.S!)
Every time her washing machine drained, she could hear a “glug lug lug” sound from the kitchen sink.
But you aren’t sure if this gurgling noise issue is severe enough to warrant spending $70 to $120 per hour (the average cost of a plumber before trip fees and materials)
A blocked drain or a vent pipe usually causes this issue. Sometimes, it can indicate a damaged sewer main line or a P-trap problem—leading to toxic gas backup or water overflowing from the toilet. Other times it may be Air Admittance Valve (AAV) issue or blockage in the septic system.
But how do I differentiate? And more importantly, how do I fix it without calling a plumber? What if my home has a septic tank, not a city sewer line?
Not an issue! I’ll share everything I’ve learned from several licensed plumbers while running a full-service construction company in Phoenix, AZ.
Let’s dive right into it!
Understanding Wet Vented Plumbing Systems: Washing Machine and Sink on the Same Drain Line
A wet vent is a pipe that doubles as a waste pipe and a vent simultaneously. These days, it’s common for the washing machine to share drain lines with the sink as it cuts down on the cost of plumbing and labor.
The gurgling sink phenomenon can happen if your laundry room is wet-vented. If the drains are close (like your sink and washer), they are usually vented through the same drain mainline and the vent pipe. If there’s a clog in the drain or vent pipe, the sink can gurgle when the washing machine drains. If your laundry room is near the kitchen, you might hear a gurgling sound from the kitchen sink.
How to Diagnose the Problem and Fix Sink Gurgling When Washing Machine Drains
The most important question is to ask:
Does the gurgling affect only a particular sink or multiple plumbing fixtures?
A specific sink drain is clogged if the blockage affects a particular sink.
If you don’t find any clogs, it’s possible that the Air Admittance Valve (AAV, if you have one) or the P-trap needs to be replaced.
If your home has a sewer system:
If all the sinks or multiple plumbing fixtures (like the bathtub or the shower drain) in your home gurgle, this could indicate a main sewer line block. You might also experience water draining slowly or water back-ups in the shower, bathtub, or sink.
If your home has a Septic system:
You could experience backups if your septic tank is full. The United States Environment Protection Agency (EPA) recommends emptying the tank every two to three years by mechanical pumping. Also, we have noticed quite a few cases of sink gurgling when something clogs the filter in the septic tank.
No matter your situation, we’ll guide you step-by-step to help you fix the gurgling sink. You can use the above tips to narrow down the issue and skip to the relevant fixes below.
1. The Problem: The Sink P-trap is Clogged, Missing, Cracked, or Empty
What is a P-trap: A P-trap is a u-shaped bent waste pipe that connects the sink’s drain to the sewer system or septic tank. It also stops dangerous sewer gases like hydrogen sulfide and methane from entering your home.
How to identify if this is your problem: The sink is likely not vented if you have an older S-trap. When your washer drains, it tries to draw the air from the nearby sink causing the gurgling noise. If you have a modern P-trap: Along with the noise, you might also sometimes experience water backflow, or the water in the sink takes longer than before to flow down. Also, the P-trap has likely clogged if your tub smells like rotten eggs.
2. The Fix: Inspect or Replace the Sink Drain P-trap
Ensure your sink drain has a P-trap: Shine a light down the drain to see if water stands in the pipe. It might only be installed if you see the pipe and no water.
Refill the P-trap: The P-trap can dry if you haven’t used the sink or nearby plumbing fixtures in a few days. A dry P-trap might be one of the reasons behind the nasty sewer smells. In this case, simply pouring water down the drain should do the trick.
Ensure there are no cracks: A P-trap can leak at the connecting nut, or the pipe can develop cracks. Tighten the bolts and try using plumbing tape to fix the leak. If it’s apparent it cannot be fixed, replace it.
Here’s how to effectively clean your P-trap:
- Turn off the water faucet and place a bucket directly under the p-trap.
- Hold the connecting pipe and unscrew the p-trap nut using a plier to remove it.
- Depending on how full your P-trap is, some water will spill out. The bucket we placed in step 1 will collect the water.
- Clean the trap using a bottle brush
- After cleaning, line up the pipe correctly and screw the trap into its place.
- Turn on the faucet to check for leaks. Tighten the bolts until there are no leaks.
If your P-trap is underground or inside your wall, you need to call a professional.
3. The Problem: The Air Admittance Valve (Auto-vent) is Not Installed or is Faulty
What is an Air Admittance Valve, AKA Studor valve: This one-way mechanical valve installed after the trap helps address the negative air pressure when a fixture is drained (like when the washer drains.) Sometimes, if you can’t (or don’t want to) vent through the roof line, you can use it for proper ventilation and prevent sewage gases from entering your home. It is typically used at an island sink or to avoid roof penetrations.
How to identify if this is your problem: If your sink drains very slowly, even when you’ve ensured there are no clogs, installing an AAV can help dissipate negative pressure caused by the washer draining—thus eliminating the loud gurgling noises from the drain. If you have an existing AAV, it may be time to replace it.
4. The Fix: Install or Replace the Air Admittance Valve (Auto-vent)
Expert tip: While most states allow the use of AAVs, some state and local building rules prohibit its use. Check with your local Authority Having Jurisdiction (AHJ) to find the most up-to-date information.
Here’s how to install or replace an AAV, also called a cheater valve:
- Disconnect and remove the trap bend using pliers.
- AAVs are typically placed between the P-trap of a fixture and the drain line. Ensure to install it at least 4″ above the horizontal branch.
- Measure, cut, and chamfer the pipe accordingly.
- Install the assembly and attach the drain pipe.
5. The Problem: The Bathroom or Kitchen Sink is Clogged
What causes a clog in my sink? The most common causes of a shower drain clog are human hairs, soap scum, and hard water. Hairs can restrict water flow and stick to grime and soap scum to worsen the problem. The soap can mix with the hard water to form a soap scum that sticks to the inner sides of the drain. If your area has hard water, calcium and iron can stick to the sides of the drain.
6. How to Unclog the Kitchen or Bathroom Sink Drain
6.1 Easy Fixes: Remove Visible Obstructions Using a Coat Hanger, Hot Water, or a mixture of Baking Soda With Vinegar
Remove the drain cover. Pour hot water around the edges. This can help dissolve the build-up of soap scum. If you’ve PVC pipes, skip this step, as the heat can damage PVC pipes. Remove the soap scum and hairs. You can use a flashlight if nothing is visible.
We hear you asking:
Can I use a wire coat hanger to clean the drain? Yes, you can use a coat hanger if the clog is near the surface of the drain. We’ve seen some plumbers’ advice against it since it can get stuck, worsening the clog. But in our experience, it’s alright to do so as long as you’re careful about it.
Alternatively, you can also try mixing 1⁄3 cup of baking soda with 1⁄3 cup of vinegar and flush it down the drain. Cover the drain and let it sit for 15 to 30 minutes. Pour boiling water down the drain. The bubbling reaction from this chemical reaction can sometimes help break up the grease or oil residues.
6.2. Plunge the Sink
A plunger is a simple plumbing tool that uses suction and pressure to remove a blockage in the drain.
Use a wet rag or duct tape to block the overflow opening on the front wall of the sink. To do this, you may need to remove the cover on the overflow tube.
If you don’t seal the drains, the air pressure can escape through other drains—making our plunging process less effective.
How to (correctly) use a plunger to plunge a sink drain:
- As mentioned above, ensure you’ve sealed the overflow using a wet rag or duct tape.
- Cover the drain opening completely with the plunger. The tighter the seal, the better. Try using a silicone lubricant if you don’t get a good seal.
- Fill enough water in the tub till the plunger cup is covered.
- Thrust the plunger up and down. Repeat this process a few times.
- If the water drains away, the unclog has been successful.
Pro-tip: We don’t recommend using chemical cleaners because they can cause damage to the plumbing, mix with the water supply, and be a hazard to us and the environment. To top that, they aren’t even very effective in removing clogs.
6.3. Plunging Doesn’t Work? Try Unclogging With a Drain Snake Auger (Plumbing Snake)
What is a Drain Snake?
A drain snake is a flexible auger that can help remove clogs when a plunger doesn’t work. The coiled-shaped metal wire can break up obstructions to enable water to flow again.
To unclog a sink drain, you’ll need a hand auger.
How to Unclog With a Drain Snake or a Closet Auger
Most augers can reach up to 25 feet—so you can easily find one for your needs. Crank the auger until you experience some form of resistance. Gently push the auger back and forth a few times to break down the clog. Then, remove the auger and run the water for about 5 minutes to flush the clog.
7. The Problem: The Plumbing Vents Pipes/Stack are Inadequate, Missing, or Clogged
What is the vent stack? The vent pipe is a vertical pipe located on your home’s roof. Its advantages are two-fold:
- It regulates the airflow in your plumbing system. The drain pipes cannot move the waste and water without proper air circulation.
- It removes sewer gases. Sometimes, these foul and dangerous sewer gases can return to your home. If you can smell strange gases, it can be a tell-tell sign of an issue with the vent pipe.
What causes the air vent to block?
- Common things that block the vent pipe are leaves, debris, insects, and sometimes—dead mice and nests (yes, we’ve seen the last two!)
- Your sink drain might gurgle when the washing machine drains, especially in cold weather, because, in colder climates, the water condenses into the ice near the air vent—thus blocking it.
- Sometimes, a contractor can forget to remove the caps on the vent pipes after running a pressure test or something.
- There are structural issues, such as the wrong slope of the horizontal venting system in the attic.
8. The Fix: Unclog the Blocked Vent Pipe/Stack or Install Sufficient Air Vents
If unclogging the sink doesn’t work, the issue is likely a clogged vent pipe.
How to clear a blocked vent pipe?
- Clearing a blocked vent pipe will require you to get on the roof—so make sure you’re comfortable doing that (or call a handyperson/plumber)
- If you’ve multiple vent stacks, look for the one near the bathroom where the bubbling or gurgling happens. If you can see only one pipe, multiple vents have been combined into one.
- Remove any leaves or debris you may find at the surface.
- Use a thin flashlight to look further down. If you see any obstructions, such as dead mice or insects, try removing them with a wire hanger.
- Pour down the water in the vent using a garden hose.
- Consider installing a screen over your vent pipe. Keeping foreign objects out of your vent pipe prevents costly plumbing repairs.
In some cases, we’ve seen examples when the plumber did not properly vent the drain. I specifically remember an incident where the plumber should have installed a Sanitary Tee instead of the 90 or ¼ Bend and then installed an Air Admittance Valve as high as possible above it.
9. The Problem: The Sewer Line is Clogged
Your main sewer line may be clogged. A tell-tale sign of this is multiple plumbing fixtures in your home are bubbling, you hear a strange gas smell, or there’s water backup. At this point, we recommend calling a professional sewer repair company. They can use hydro-jetting to shoot up to 4,000 PSI of water through the pipes—enough to break down tree roots or anything clogging the sewer line.
10. The Problem: The Private Septic Tank has Blockages, clogged filters, or is Full
If the line from (or to) the septic tank to a drain field is partially blocked, it might usually work until there’s suddenly increased water usage.
Does your shower, tub, or sink gurgle only when it’s laundry day, when it’s raining, or when you have guests over? A partially clogged waste piping can certainly be the issue. This can also lead to sewage smells or backups in your home.
A common question we get asked is:
“Shouldn’t we see issues from other plumbing fixtures (showers, dishwashers, toilets) if the issue was the septic tank?”
Well, it depends.
Not always, because a lot of toilet flush stays in the lines and doesn’t make its way down to the main until several flushes later. The volume of water may be the same, but the shorter distance between the draining fixtures and the main increases the obviousness of the symptoms.
11. The Fix: Pump/Empty the Septic Tank and Unclog Filters
The United States Environment Protection Agency (EPA) recommends emptying the tank every two to three years by mechanical pumping. Also, we have noticed quite a few cases of tub gurgling when something clogs the septic tank filter. Pumping the tank and cleaning the tank filter should do the trick.
Also, check for the following:
- Blockages in the line from your home/building to the septic tank.
- Solids blocking the septic tank inlet or outlet.
- Clogs in the septic tank filter
12. Nothings Works, and the Sink Drain Still Gurgles? Here’s What to do When Everything Fails
In our decade-long experience, the above tips should solve the issue in most cases. If it doesn’t, you may have an edge case. Here are some additional tips:
- Check for vacuum breakers at drains: Sometimes, old plumbing fixtures with no proper ventilation can have a vacuum breaker one-way valve. A malfunctioning or broken valve can also lead to this noise.
- Improperly installed or no ventilation: If your home is new, it’s possible that the vent has not been installed or is incorrectly installed.
- Inadequate ventilation: If you don’t see a plumbing vent stack pipe over your home where the sink is located, they might have insufficient or improperly installed ventilation. It’s also possible that the plumbing fixture is too far away from the plumbing stack.
- Cast iron pipes can restrict water flow more easily: If your home has old cast iron pipe plumbing, it may be more prone to clogs. It can quickly corrode and build up more minerals and waste. Consider replacing it with ABS or PVC pipes and increasing the diameter of the pipes.
- If everything fails, it’s time to call a professional licensed plumber. They can perform a visual inspection and use a drain camera to investigate the issue further.
13. Outing Bad Advice From a Popular YouTube Video: What Not to Do If Your Sink Gurgles
One of our long-time clients was dealing with the issue of the washer drain backing up to their kitchen sink.
They researched this issue online and shared this popular YouTube video with us:
This 10-minute long video has about 150k views and details how they solved it using a washing machine drain-out kit suitable for 1¼” and 1½” waste pipes.
While it works, it’s easy to overlook the fact that the publisher is based in the U.K., and this technique would pass an inspection there.
But since a vast majority of our readers and clients are from the Land of the Liberty, we don’t recommend doing so and here’s why:
Doing so bypasses the trap. The bacteria and sewerage stench can be a potential health hazard.
I hear you:
“But there’s no smell…”
This is probably because of the non-return valve.
You still have a clear path from the dishwasher outlet hose to the drain out of the sewer. It wouldn’t pass an inspection here in the United States. We’ve heard from our Aussie friend it likely wouldn’t pass an inspection in Australia either! If you’re going to do it anyway, put a second trap between the drain out.
As always, make sure you check with your local building codes and be aware that advice can be geo-specific.
Frequently Asked Questions (FAQs)
Why Does My Sink Gurgle but Drains Fine?
This issue is caused by a partially or entirely clogged drain and/or an improperly vented drain. A blockage in the pipe creates suction, which pulls on the water in the p-trap, creating a gurgling sound as water appears in the drain.
Why does the sink gurgle after installing AAVs?
The likely cause is a blockage downstream of the kitchen. The Air Admittance Valve (AAV) allows air to enter but not exit the plumbing system. Vents equalize the backside pressure of plumbing systems, which are neutral pressure systems. As the water from your washing machine drains, a blockage creates a pressure buildup that AAV cannot release. Removing the Air Admittance Valve allows the air to escape up the vent pipe.
Why is the Water Going From My Sink into my Washing Machine?
This is likely because you have got a clogged main drain line or your washing machine outlet needs to be correctly installed. In many (American) homes, a washing machine and kitchen sink share the same drain lines leading to this problem. You can try plunging the sink with a plunger or a drain snake. If the clog is deeper, it might be time to call a professional plumber. Alternatively, it’s also possible that the washing machine outlet is incorrectly installed. Before delivering the washer hose into the spigot under your sink, ensure that the hose rises up to a high point, such as over the top of the base unit, through a hole near the top or fixed at a high level.
Why Does My Kitchen Sink Smell When Washing Machine is on?
The smell is likely caused by an improperly vented drain, which can push sewer gases past the trap into your kitchen sink leading to a rotten eggs or cabbage (hydrogen sulfide) like smell. The fix is to properly vent the drain by removing the blockage from the existing vent or correctly connecting the drain line to the existing vent. Alternatively, you can also install a new vent on the roof or use an air admittance valve if your sink is located on the upper floor of a building.
Why Does My Double Kitchen Sink Gurgle?
Large double sinks connected in a long horizontal run tend to fill up the drain pipes quickly. This slows down the draining of the sink. This gurgling sound is caused by air being drawn through the water, which should be sealing the P trap.
Can The Washing Machine Drain Into A Sink?
Yes, the washing machine can drain into a sink by connecting the washing machine’s drain hose to the sink drain. In addition, a T-fitting or Y-fitting would be required to allow water to flow into the sink while also allowing normal drainage. Some plumbers don’t recommend this setup if your utility sink doesn’t use a 2″ pipe, as it wouldn’t be code compliant. However, in our opinion, if your sink is deep or large enough, this shouldn’t be an issue. As always, don’t forget to check your local building codes.
Why Does Water Come Up The Sink When The Washing Machine Is On?
One likely cause is something blocking the drain, like soap or hair, which is causing the water to not drain properly and overflow. Alternatively, some older homes have 1½-inch washing machine drain lines, while most modern washers are designed for 2-inch drain lines. If the pipe that drains your washer is smaller than the water capacity of the washer, the excess water may overflow into the sink.
Is a Gurgling Sink Dangerous?
A gurgling sink indicates a clogged drain and/or improperly vented drain. In most cases, this is not dangerous. However, if you can also smell a strong sewage smell, this could point to a more serious health issue like a sewage leak. We recommend you call a licensed plumber or a professional at this point.
Why Does My Kitchen Sink Drain Make a Gurgling Sound When it’s Windy Outside?
This can be caused by the winds creating negative air pressure in your waste and vent plumbing system. This changes the flow of water and air in the system, leading to a gurgling sound. This issue might be exaggerated if the roof stack vent is improperly installed.