Why Does My Downstairs Toilet Gurgle When Upstairs Toilet Is Flushed?

Is it really an issue of grave importance if your downstairs toilet gurgles when upstairs toilet is flushed? Sadly, this could be indicative of a bigger problem and not just a minor nuisance. So, why does my downstairs toilet gurgle when upstairs toilet is flushed?

When a toilet gurgles, suction is building up in the drain line, which causes an airlock. Since the same pipe connects to both your upstairs and downstairs toilet, there may often be some clog in the mainline connecting to the neighborhood sewer.

Downstairs toilet gurgle when upstairs toilet is flushed

When the suction releases in the pipe, then air will be pushed back via the drainpipe and into your downstairs toilet, which will cause bubbles to form in your downstairs toilet and can cause a gurgling drain.

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What Causes the Gurgling Sound?

In a working drainage system, air will flow throughout the pipes, which will negate any air suction and let your waste move down and out into the drain. However, if your toilet is making a gurgling drain sound, then that means that there is some negative air pressure in the line.

This suction/negative air pressure clog can be attributed to two possible sources: the main sewer line or your house’s vent stack, the pipe that lets sewer gases move up via the roof).

Based on how nasty the clog is, you can either fix it yourself or hire a plumber to fix it for you. While the gurgling toilet may be irritating, it can eventually cause greater problems if it comes from a faulty sewer line. If you ignore the problem, the toilet clogs may end up causing your waste to flow back up into your toilets, showers, or bathtubs.

Here are five possible solutions for when your downstairs toilet gurgles when upstairs toilet is flushed.

Step 1: Use a Plunger to Dislodge More Minor Clogs

Plunger to dislodge more minor clogs

If the main problem is the drainpipe, then if you plunge your toilet, you may be able to create enough pressure to unclog your pipes. This technique will usually work for lighter clogs that got lodged in there from flushing cotton swabs that got stuck in your drainpipe. Almost all bathroom appliances (your sink, bathtub, toilet, shower) all use the same drain line that runs from your toilet.

As such, you should seal these drains off with duct tape before plunging. If you do not, your plunger-induced pressure may move through your other bathroom appliance openings rather than dislodging the clog.

When the toilet is filled with water, you should lodge the plunger’s head to the drain hole near the bottom of your toilet bowl. It should take about 10-15 plunges before you unclog the pipe. If your toilet is still gurgling, then you should try some of our other suggestions.

For this method, it will help to select the proper plunger as well. This plunger with a sold rod and thick rubber cap is what I recommend for this job.


Step 2: Check If Your Neighbors Have the Same Issue

You may want to check if your neighbors have also had issues with their toilet gurgling. If you are not the only one on the street with the issue, it may be a problem with the community sewage system in general, and you may need to call your municipal sewage services to possibly fix the main sewer. While this may be a major systematic problem, this also means that you will incur none of the repair costs.

Step 3: Use a Plumber Snake to Clear Your Drain

If you have a plumber’s snake, you can usually use this to pull out your drainpipe’s clogs. A plumber’s snake has a long cable with bladed heads to cut through lodged-in clogs. You use your hands, crank, motorized system to operate your plumber snake.

If you are using a manual toilet snake, you will insert it in the toilet bowl, and the head would slowly flow down through the drainpipe and use its blades to cut through clogs.

This snake has only about 5-15 feet of cable reach, so it may be difficult to reach deeper clogs. For this, it may be best to purchase a motorized model that can reach clogs up to 100+ feet down the pipe. The auger on a motorized snake is usually too big to go through the toilet bowl, so often, you would have to remove the toilet and insert the snake directly through the drainpipe.

When you turn the machine on, it will slowly work its way down, and its sharp blades will cut through all those clogs. Instead of buying one of these, it often only costs $40-50 per day to purchase one, which will be more cost-effective than calling a plumber, which can cost up to $400-500.

This usually will clear your toilet gurgling since it will rip through any cogs in the drainpipe. However, if it does not, you should likely move on to the next step and check your drainpipes.

Step 4: Check Your Vent Stack for Clogs

Check your vent stack for clogs

This can be done either before or after you snake your drain, but it may be best to do it after since drainpipe clogs are usually the issue. However, it is also common for your home’s vent stack clogs to restrict airflow throughout your house and subsequently into your house, which can cause gurgles.

Checking the plumbing vent stack for clogs means that you will have to work on the roof, so it may be best to call a professional for this step. Usually, the clog will be 8-10 feet from the top of the plumbing vent stack pipe and visible to you or your hired help.

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