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Why Does My Sink Gurgle When the Toilet Flushes? 3 Reasons

bathroom sink

Sometimes when you flush your toilet, you can hear a distant gurgling sound. Usually, the sound is emanating from the closest sink or even your kitchen sink a couple of rooms away. Some people think that this problem is harmless, and that gurgling is just a quirk of your plumbing system, but that is not the case. If your sink gurgles after you flush a toilet, your plumbing is trying to tell you something. The sink is not supposed to gurgle after the toilet flushes, and the sound tells you that something is wrong.

A gurgling sink might seem innocuous, but it can signal a larger problem with your plumbing. Oftentimes, fixing the problem is simple, and the solutions can be done by yourself at home. In other cases, the problem might be larger and deeper than you first anticipated. Here are three reasons why your sink could be gurgling when you flush the toilet and how to solve each.

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The 3 Reasons Why Your Sink Gurgles When the Toilet Flushes

1. Blocked Vents

Whenever water leaves your home via something like a sink or a toilet, a ventilation pipe adds air in behind the water. Without a ventilation pipe, the water would leave behind a vacuum. Without flowing air, your pipes will contain small pockets of vacuum, which can play havoc on your plumbing system. Your pipes are not designed to operate with a vacuum inside of them. Healthy pipes want to be filled with either water or air.

If you have a clogged ventilation shaft, the air will not be able to properly enter your pipes to neutralize the vacuum. The result is that the pipes will try and suck in air from other openings, like your kitchen sink. If the pipes begin pulling air into the system through your sink drains instead of the ventilation shaft, it can cause any water left over in the pipes to move and gurgle.

Solution: Check Ventilation for Obstructions

Most homes have a ventilation pipe in the roof that connects to the main drain line below. You will want to climb up to the roof and check the pipe for any signs of obstruction. Leaves and sticks can fall into the opening and block air from entering. Sometimes animals can also take up residence in or around your ventilation stack. Birds’ nests can quickly clog up a ventilation pipe and create issues inside.

Sometimes homes have other smaller vents around the roofline that also feed into the plumbing system. Check any vents, louvers, or small openings for signs of weeds, leaves, or debris that could be impeding airflow into your home. Simply clear out the blockages and check to see if the gurgling stops.

2. Blocked or Clogged Pipes

close-up of water leaking from the white sink pipe
Photo Credit By: Andrey_Popov, Shutterstock

Another problem that can cause sinks to gurgle when you flush the toilet are clogged pipes. Even if your toilet is flushing and your sink is draining, you could have a partial clog far enough down the pipes that you don’t immediately notice. If you notice slow drainage in conjunction with the gurgling, there is a good chance that something is clogged.

Solution: Plunge or Unclog the Gurgling Sink and the Offending Toilet

The easiest solution is to unclog the blockage from the inside. You can plunge the toilet and plunge the sink where the gurgling is coming from. You can plunge a sink the same way you plunge a toilet (though you might want to disinfect your plunger if you use it frequently in your toilet before shoving it into your kitchen sink.) You can also buy liquid pipe cleaner and pour it into your sinks to alleviate any clogs. You should never pour liquid drain cleaner into a toilet. Chemical drain cleaners are not designed for use in toilets. Only use them on the sinks.

After you are done plunging your toilet and unclogging the nearby sinks, flush and check to see if the gurgling has gone away.

Your slow drainage issues should have abated, and in many cases, the gurgling sound will also dissipate after the drains are cleared.

3. Lurking Plumbing Issues

If the most common solutions don’t fix your gurgling problem, it could betray a deeper issue lurking in your pipes. Home plumbing systems are more complicated than most people know. There could be various issues hiding out of sight that will require the use of a professional plumber. Some deeper issues can include a busted main drain line or a clogged sewer line. A gurgling sink is annoying, but it might not sound like a serious issue. Unfortunately, it can be a small symptom of a much larger problem. Ignoring major plumbing issues can lead to the issues growing over time until you have a sewage nightmare on your hands.

Solution: Call a Plumber

The only viable solution to these more serious problems is to call a plumber. Plumbers will be able to diagnose the problem in more detail and reach areas of your pipes that you cannot get to on your own. Plumbers will be able to snake the main drain line and check it for damage. They will also be able to tell if the potential clog could be in the main sewer line, which runs from your house out to the road where it links up with the water main. It may not sound necessary to call a plumber to deal with a gurgling sink, but a busted drain line, clogged sewer line, and major ventilation blockages can lead to enhanced damage over time, and then a gurgling sink will be the least of your problems.

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Gurgling Usually Involves The P-Trap

Male Plumber's Hand Repairing Sink Pipe Leakage With Adjustable Wrench
Photo Credit By: Andrey_Popov, Shutterstock

Any gurgling in your sink usually denotes a problem with the p-trap. The p-trap is a critical component of your sink. It is a curved portion of the piping that is designed to hold water. The water acts as a seal that prevents sewer gasses from coming up through your pipes and causing your house to stink. The gurgling you hear is usually caused by air passing through this water and causing a sound. That is bad because nothing is supposed to be able to go through the P-trap. That means the seal is not working as intended. When in doubt, check the p-trap for debris and make sure that it is installed properly and that if you have an air admittance valve on your p-trap it is also in working order.

An air admittance valve is sometimes installed to help add air into the pipes without the use of an overhead ventilation pipe. Air admittance valves can last between 20 and 30 years, but sometimes they go bad, and it could be the source of your phantom gurgling noise.

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Hopefully, you can resolve your gurgling sink troubles with little time, money, or effort. Unfortunately, you might be required to call in the help of a professional to squash the issue for good. Ignoring a gurgling sink is unwise as it is a sign that something in your plumbing is not functioning as it should. Jumping on one of these solutions as quickly as possible is the best course of action to ensure the issues remain minor.

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Featured Image Credit: Brett_Hondow, Pixabay


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