Bathtub Drain Gurgles When Toilet Is Flushed (Fix It Now!)

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Have you ever been in your bathroom, flushed the toilet, and then heard an unexpected gurgling noise coming from your bathtub or sink? The combination of a flushing toilet and a gurgling bathtub might seem innocuous at first glance, but it can hint at underlying issues within the intricate network of plumbing.

When the toilet flushes, the gurgling noise from the tub drain is usually triggered by air trapped in the plumbing pipes or vents. This can occur as a result of clogged vent stacks, malfunctioning sink vents, clogged sewage lines, limited drain valves, rusted cast iron pipes, or poor plumbing venting. Cleaning the vents, plunging the toilet, inspecting the roof exhaust pipes, or enlarging the pipe size can all be necessary to resolve this issue.

What Does It Mean When You Flush the Toilet and The Bathtub Gurgles?

water is backing up in the drains the tub is making a gurgling sound

Faulty Sink Vent

A fault sink vent is a common source of gurgling sounds. The sink vent helps to remove any water and air from the drain pipes, allowing the plumbing to function effectively. If this vent gets clogged or broken, your drains may begin to gurgle.

Run water through the faucet and listen for gurgling sounds to test this. If you hear these noises, it is possible that your sink vent is clogged and must be cleaned. You may use a plumbing snake or manually empty it to accomplish this.

If you also notice that the sinks are draining slowly, that means there’s poor venting. If the vent is blocked/clogged, it does disrupt the pressure in the plumbing system.

Clogged Sewer Line

If your bathtub drain gurgles whenever you flush your toilet, there is likely a clog in the central sewage system. This may result from tree roots, garbage accumulation, or other things trapped in the pipe. You’ll need to hire a licensed plumber to clear the obstruction and restore appropriate drainage.

Narrow Drain Valves

If you have gurgling drains when flushing the toilet, it’s likely the drain pipes are too narrow. This might generate a suction that draws air from the sewage system and cause the drains to gurgle. Some of the waste from the toilet will undoubtedly stick to the pipe walls.

This waste tends to decompose over time, resulting in a solid blockage. This will not physically clog your pipes but significantly narrow them. When even a small amount of water enters your bathtub drain, pressure develops, and air gurgles.

If you’re fortunate, your plunger may be able to dislodge some of the solidified debris and enlarge the pipes. Use rubber plugs to seal the drains of your bathtubs, sinks, and other fixtures. Thus, your whole plunging power would remain within the pipes.

Using a toilet auger is recommended if the gurgling remains after three to four rounds of plunging. You can also use a toilet auger to clear the clogs. It works similarly to a standard drain auger but is fitted with a more extended arm to push the wire deeper. However, be careful when using the auger so as not to scratch the toilet bowl.

Plumbing Vent System

A problem with the vent pipe is among the common causes of gurgling sounds from the bathtub drain. The vent pipe facilitates the free movement of water in the plumbing system. Water won’t flow properly if there is a blockage or a leak.

Air fills plumbing pipes if no water is available. All plumbing systems are equipped with ventilation mechanisms that exhaust air through the roof. If the plumbing vent system is obstructed, bathroom drains may gurgle. The plumbing pipes in a bathroom are all linked to one system.

When a fixture in the plumbing system becomes clogged, you will notice a gurgling sound.

Rusty Cast Iron Pipes

Before the introduction of PVC and ABS and PVC pipes, cast iron was commonly used in plumbing systems. Cast iron, unlike its successors, is prone to rust and hard to cut without assistance.

If your home was constructed before the 1980s and you still have cast iron drain pipes, it is likely that they are rusted and should be replaced. There may be some leaking at the joints or in the gaps of the pipes. In this situation, you should contact a professional plumber to replace them.

Problems with the P-Trap 

P-traps are a specific type of plumbing trap designed to prevent foul odors and gases from entering buildings through drains. They are commonly found under sinks, bathtubs, showers, and other plumbing fixtures.

The “P” in P-trap refers to its shape, resembling the letter “P” when viewed sideways. It consists of a curved section of pipe that holds water, creating a seal that blocks sewer gases and odors from coming back up through the drain into the living space.

Here’s how a P-trap works:

  • Water Seal: The curved shape of the trap holds a small amount of water at all times. This standing water acts as a barrier, preventing sewer gases and odors from traveling back up through the drain and into the room.
  • Preventing Clogs: Additionally, the trap’s design can catch debris that gets washed down the drain, preventing it from traveling further into the plumbing system and causing blockages.

P-traps are often made of PVC (polyvinyl chloride), ABS (acrylonitrile butadiene styrene), or metal (such as brass or stainless steel), and they are a standard component in most plumbing systems due to their effectiveness in maintaining a sanitary and odor-free environment inside buildings.

Gurgling issues may occur when a quick surge of water in the pipe, such flushing a toilet, produces an upward pressure that backs up wastewater in a plumbing drainage system. This may push air and water bubbles down the drain, making that distinctive gurgling noise.

Trapped Air in the Vent

Vent pipes play a crucial role in regulating air pressure within a plumbing system by allowing air to enter. These pipes run from the drainpipes upwards through the roof, facilitating the movement of wastewater and odors away from the building.

If vent pipes become obstructed, gurgling noises may arise. This happens when air is unable to exit through the vents, causing it to push through the drains instead. This shift in pressure creates a noticeable gurgling sound.

How to Fix Bathtub Gurgles When Toilet is Flushed?

Now that you know the different causes of noise when the toilet is flushed, lets have a look at some of the different ways to fix this problem.

1. Pump Air Out Using a Plunger

One of the reasons that cause a bathtub drain to gurgle when flushing the toilet is air stuck in the pipes. Using a plunger will remove the air in the pipes, drains, and even unclog the toilet.

This is an easy and quick method to sort your plumbing issue without involving a plumber. You only need to purchase a few things like duct tape and plunger, and you are good to go.

Here’s how to pump air out

  • Use duct tape to close the drains. Cover the drains and pipes to prevent air from getting in.
  • This process ensures that the force of the plungers stays within the pipe. Ensure the bowl of the plunger is totally submerged in water before you begin the process.
  • Start plunging for a few minutes, then flush the toilet and listen to whether there is the gurgling sound. If it’s still there, start plunging again.
  • Plunging removes air or any other obstructions stuck in the drains or the pipe. You can use Neiko 60166A Toilet Plunger for this process.

2. Check the Venting System

If the problems still persist even after continuous plunging, then you need to take a look at your venting system.

Due to the location of the venting system (the one on the roof), it means leaves or dirt may get into the pipes and become a problem. You need to continually clean the vent to remove the dirt and allow air to go through easily.

Cleaning the pipes is not hard, but it may require a bit of effort, which is worth it considering the nuisance that clogged vents bring. You will need your hose pipe or any other material that can force water through the vents and a plumbing snake.

The process involves:

  • The plumbing vent is often placed above the bathroom; safely access the roof to find it. You’ll need to take off the vent’s cap if it has one. Occasionally, rodents, birds, or other animals may become trapped there. Debris such as leaves might also jam the pipe.
  • Peek down the pipe with a flashlight to see if you’re able to see the obstruction. It is possible that it is too deep for you to see. If the clog isn’t too deep, use a drain snake to clear it out.
  • Simply insert the plumbing snake into the vent’s pipe until you reach objects blocking it.
  • Then work the plumbing snake back and forth to altogether remove the clog.
  • Once you have it out, use a jet hose set to “jet” to rid of any other trash that is still there.
  • You can try to remove the clog with the hose if you are unable to see it or reach it using a snake. That’s usually all you need. However, you might need to use an auger or perhaps hire a professional if the clog is something tough to remove.

Some blockages may be stubborn and hard to reach, so you will need a FlexiSnake FSMPD Drain Millipede plumbing snake to remove them.

3. Increase the Diameter of the Pipe

Bathtub Drain Gurgles When Toilet Is Flushed v_1_1

Another possible solution to your gurgling problem is increasing the diameter of the pipe. Extra toilet paper can be a problem to a smaller pipe.

So, you need to increase its diameter to ensure that waste flows through without clogging. Most toilet drain pipes are 3 inches in diameter; raising it to 4 inches allows more waste to pass through.

You will need to replace the existing pipe with the 4 inches. The process is not laborious if you are ready for the work; it’s actually an excellent DIY project that saves you a lot of money.

Increasing the diameter of the pipe is not only a “now solution” but can also benefit you in the long run. You will need the help of a professional because fixing the pipe require technical knowledge.

4. Use Chemical Solutions

You can also use chemicals to deal with bathtub gurgles when the toilet is flushed. Certain chemicals can help clear the problem and give you peace of mind.

There are Chemical solutions that you can easily make at homes, such as a drain cleaner, which consists of water, baking soda, and vinegar.

All you need to do is boil a lot of water, almost a gallon. A lot of water ensures there is enough force to remove the clog. However, ensure the water is not too hot because it may damage the toilet’s porcelain.

Pour your vinegar and baking soda into the toilet to remove the clog. The combination of the products creates a solution that is effective enough to dissolve the clogs.

However, in the case of clogs, such as a rock or toys, the solution may not work.

Once you have poured the solution, pour the hot water into the toilet, starting from the waist level. The hot water ensures that the clogs are pushed out of the drains.

Lastly, allow the mixture to stand still until morning. This will give it enough time to dissolve the clogs and push them down the drain.

Remember, this method will only work on clogs from organic material. Therefore, if you still hear the bathtub gurgling, then the cause is a much bigger object.

You can also purchase a drain cleaner such as Green Gobbler Drain Clog Dissolver if the problem is not hard clog. The process is simply pouring in the drain cleaner according to the manufacturer’s instructions

Ensure you allow the solution to stand still for some hours before you use a plunger.

Also, ensure you open windows to allow air to flow in since the chemicals can be quite unbearable.

5. Use a Coat Hanger to Remove Clogs Near the Drain

Another material to help you remove clogs is a coat hanger. This may seem like a strange method, but it actually works.

The steps involve:

  • Straighten the hanger, then cover the end using a rag to prevent it from damaging the toilets’ porcelain.
  • Then guide the straightened hanger, which is wrapped down the drain until you reach the obstruction.
  • Then twist the hanger severally to break the clog and remove it.
  • Finally, flush the toilet to push the small pieces of clog down the drain to the sewer.

Remember, this method only works for clogs that near-reach. You will need a plumbing snake for the hard to reach clogs.

6. Replace Rusty Cast Iron Pipes

Before the introduction of ABS and PVC pipes, cast iron was a commonly used material in plumbing systems.

However, unlike modern alternatives, cast iron pipes are prone to corrosion. When these pipes corrode, their surfaces become rough, leading to a higher accumulation of waste and mineral deposits.

As mentioned earlier, when narrow pipes encounter flowing water, they tend to build up air pressure. In the case of corroded cast iron pipes, this increased pressure causes air to escape through the drain, resulting in the bothersome gurgling noises.

Replacing these pipes requires a significant level of technical expertise. Hence, it is advisable to seek the services of a professional plumber for this task rather than attempting it DIY.

7. Call a Plumber

If you have tried all the methods, but the problem still persists, then you may need to call in a plumber. A plumber will inspect your bathtub, drain, and the toilet and know what needs to be fixed.

Final Thoughts

In conclusion, gurgling sounds coming from your bathtub drain when you flush the toilet is a telltale sign that something is wrong with your plumbing system. Ignoring this issue now can result in more serious issues later on.

Gurgling can be caused by a number of things, including blockages, clogs, venting issues, or plumbing layout problems. But determining the exact cause need a professional examination.

It is vital that this problem is not disregarded, as it may worsen and result in sewage backups, pipe damage, or leaks, all of which might be hazardous to health and need expensive repairs.

The best course of action is to get expert assistance from a licensed plumber. A skilled plumber can precisely evaluate the issue, pinpoint the underlying cause, and carry out the required maintenance or repairs to get your plumbing system operating again.

Furthermore, it is important to schedule routine plumbing inspections and promptly address any problems to avoid reoccurring concerns. You can guarantee the smooth and effective operation of your home plumbing, protecting your property from any water damage and maintaining its integrity, by being proactive and taking quick action when you notice plumbing issues.

6 thoughts on “Bathtub Drain Gurgles When Toilet Is Flushed (Fix It Now!)”

  1. I have two toilets tied at a ‘Y’ on first level . When I flush , the tub drain gurgles, if I flush 3 times the poop comes up in tub. GROSS! Can a clogged vent on roof cause this ?

  2. Hi- I live in an old house. First, when I emptied to bathtub, the water in the toilet would recede. I called roto rooter and they found lots of roots in the line leading out to the city pipes.
    Now, when the tub empty’s the toilet water does not recede but when I flush the toilet, I hear noise in the bathtub and sink for a short time.
    Roto rooter says I may need to reline the basement line leading to the city line with fiberglass.
    Could there be a different issue?

    • Hi- that’s what rotorooter told me and the guy did a quick video of the line but didn’t explain what I was looking at. He said about 18,000.00$ would fix it. I’m not sure that is the problem because the vent on the roof is what other people have told me as well. I would have to hire someone to go up on a steep roof. These are old systems of course but I also think that the guy from rotorooter is looking for jobs as well.


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