Signs of Poorly Vented Plumbing Drain Lines (2022)

Solutions to a bubbling toilet or changes in the water level in the bowl.

Why is the Toilet Bubbling?

If you have air bubbles that rise up through your toilet bowl (except when it flushes) or notice the water level rising and falling, you probably have a clogged or improperly vented toilet. This toilet bubbling problem is especially true when you have an appliance like a clothes washer nearby. Your drain plumbing line is gasping for air.

If you suspect it’s just a simple toilet clog, here’s how to unclog it.

Why is the water level rising and falling?

Other explanations for toilet water levels rising and falling are that a waste pipe could be pitched incorrectly, which can make the water settle to a new level or there is a hairline crack in the porcelain in the trap that is causing a slow leak. But it’s usually the air vent that causes the water level to rise and fall.

Howdrain plumbing works

When you pour liquid from a can, you’ll notice that it doesn’t flow evenly unless you have a second opening for air. The same holds true for plumbing vent pipe. As water goes down a drain, air is needed to equalize the pressure in the drain line.

This is the purpose of a venting system. If the drain lines in your home have poor venting (as in Figure A, for example), water rushing down the drains will pull water from nearby P-traps. The drain in the toilet bowl is basically a P-trap. If the problem just started, it’s probably a blocked drain or plumbing vent pipe that needs to be “snaked” out. And since the water in the toilet is dropping and gurgling, it’s likely that the problem is near that area.

Unfortunately, a clogged or missing vent is tough to fix, since it usually requires breaking into the walls to examine the drain system. Unless you have plumbing experience, this project is best left to a professional.

Figure A: Common Example of Poorly Vented Drains

Bathroom plumbing venting in this system is missing, or the vents don’t open to “free” air.

Signs of Poorly Vented Plumbing Drain Lines (1)Family Handyman

Next, check out these 10 silent signs that you have a major plumbing problem:

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Signs of Poorly Vented Plumbing Drain Lines (2) ronstik/Shutterstock

Discolored Pipes

The next time you're in your basement or poking around under the kitchen sink, take a long look at your pipes to see if there are any signs of discoloration, especially around a union. If so, it's a strong sign there's moisture present. This may be caused by dripping from a sink or drain line, or something more serious, such as a slow leak in the supply line. If it's the latter, then you should definitely put this at the top of your to-do list. Plumbing supply lines are pressurized, which means that a slow leak has the potential to turn into a big mess fast!If you are seeing discoloration and build-up, here's how to stop leaks in plumbing joints.

Signs of Poorly Vented Plumbing Drain Lines (3)EverGrump/Shutterstock

Sewer Odor

Without getting too far into building science, a general plumbing rule of thumb is that every drain needs a trap, and every trap needs a vent. All those traps and drains are designed to prevent sewer gas from entering your home. The vents in your home should channel sewer odor up to the roof, while drain traps create a "water plug" that acts as a barrier stopping sewer odors from coming through the sink drain. If you smell sewer gas in your home, that means either a trap has run dry or a vent line has cracked. A dry trap can be fixed as easily as refilling it with water, or you may need to examine it for signs of the leak. Tracking down a cracked sewer vent can be much more difficult, as they are often enclosed in a wall, and will require a bit of drywall surgery in order to find and repair.Here's where you can learn more about how to eliminate sewer odors.

(Video) Un-vented plumbing fixtures drain faster!

Signs of Poorly Vented Plumbing Drain Lines (4)Maxal Tamor/Shutterstock

Weak Water Flow in Multiple Locations

A slow stream or low water pressure indicates an issue in distribution. If it's only occurring at one location, it's usually an issue in the faucet aerator—which is usually an easy fix. But if the water pressure is low in several spots around your home, that's the sign of a bigger problem. In that case, you're looking for a problem at the water main, in the hot water heater, or (worst case) an active leak in the supply line. If you're seeing low water pressure in conjunction with some of the other items on this list, such as bubbling wall paint, it's imperative that you take action right away.If you simply would like to have a stronger flow at your faucets, here's how to boost the water pressure in your home.

Signs of Poorly Vented Plumbing Drain Lines (5) sasha2109/Shutterstock

Slow Drain

It's no surprise that a slow drain is a sign of a problem in your plumbing. Depending on where the issue is, it may be an easily removed clog near the drain, or it could be an issue farther down the line that will require significant snaking to resolve. Luckily, a little bit of detective work should help zero in on the problem. Cleaning out a simple clog is a great DIY fix, but slow drains throughout the home are often an indicator that there may be a major issue, like tree roots, in the sewer line.Here's how to unclog a sink drain without using chemicals.

Signs of Poorly Vented Plumbing Drain Lines (6) Paul Tessier/Shutterstock

No Water in Winter

If your water pressure suddenly drops or completely ceases in the middle of winter, there's a chance that your pipes have frozen. This is a major issue and needs to be dealt with immediately.An especially common problem in homes where the supply lines run through an attic, crawlspace, or other unheated space, frozen pipes hold the biggest danger once they thaw. That ice is acting as a plug, holding back the water from rushing out any splits that may have occurred. If you think you might be dealing with this issue, step through the troubleshooting carefully, and prepare to deal with a leak. If you get lucky enough to have the frozen pipes thaw without issue (copper pipes can expand slightly without bursting), don't count on being that lucky the next time. Take steps immediately to fix the situation.Here's how to prevent frozen pipes with a combination of insulation and warm air.

Signs of Poorly Vented Plumbing Drain Lines (7) fizkes/Shutterstock

Spiking Water Bills

A sudden jump in your water bill is more than just a pain in the wallet. It's also a sign that something has changed in your plumbing system. If you haven't done anything to justify an increase in water usage (such as filling up a pool or watering your lawn more than usual) you should begin troubleshooting to find out if you have a leak. The most common source of the water bill jump is a running toilet. Many homeowners don't appreciate how much water a toilet uses; the toilet valve is essentially a garden hose going at full blast, and it's not unusual for a single running toilet to waste hundreds of dollars of water.That's why you need to know how to stop a running toilet!

(Video) How to find out if a plumbing vent line is clogged.(2021)

Signs of Poorly Vented Plumbing Drain Lines (8)Oleg RudniK/Shutterstock

Bubbling Ceiling or Wall Paint

If the paint on a wall or ceiling suddenly begin to bubble or peel off, it's most often a sign of moisture. The most common cause of this headache is a leak in either the roof or plumbing system. Should you see paint bubbling or blistering, or brown spots appearing on a ceiling or wall, it's time to begin the investigative process to find out what's wrong.Here's more great advice on how to find and repair hidden plumbing leaks.

Signs of Poorly Vented Plumbing Drain Lines (9)Gts/Shutterstock

Green Patch in the Yard

One common sign of a sewer issue is one section of your yard that's much greener than the areas around it. This is especially true if the patch falls between your house and the street, which is the most common path for a city sewer line. Leaking sewer drains can also create sunken areas in the yard as the additional fluids cause the dirt around them to compact. Whether caused by degrading materials or invasive tree roots, this silent damage to the exterior portion of your plumbing system will need to be nipped in the bud.Check out this Family Handyman article for ways to stop tree roots from plugging sewer lines.

Signs of Poorly Vented Plumbing Drain Lines (10)Family Handyman

(Video) How to Diagnose Plumbing Drain Problems | Ask This Old House

Wobbly Toilet

If your toilet wobbles when you sit down, it's a sign that something isn't quite right. Hopefully you simply need to tighten the seat. But if the bowl itself is wobbling, examine the bolts that hold the toilet to the floor. If those bolts are tight and the bowl still wobbles, then there's a chance that the wax seal around your toilet drain has failed, and water is eating away at your sub-floor.Replacing or reseating a toilet may seem like a major plumbing project, but this article breaks down the steps and shows it's not that complicated and you can do it yourself.

Signs of Poorly Vented Plumbing Drain Lines (11)Jess Rodrigues/Shutterstock

Shocking Water Color

If the water coming out of your faucets isn't clear, it's an indication there's something going on. Excessively cloudy water is often caused by air in the pipes, while yellow or brown water indicates rust. (Note that on occasion water can come into your home tainted by these materials; in older systems for example, there can be an onrush of rust in nearby homes when the fire department flushes the hydrants.) Less frequently seen is a green tint caused by extensive corrosion in copper pipes. This is a sign that it's time to inspect the system ASAP, as pipes in that state of degradation usually begin to leak outside the system relatively quickly!

(Video) Symptoms of Plugged Plumbing Vents : Plumbing Fixes


What happens if a drain is not vented? ›

Poorly-vented drain lines will not be able to effectively move wastewater and solid waste out of your building. This could lead to problems such as overflowing drains, backed-up toilets, and similar plumbing issues.

How do you test a plumbing vent? ›

Use a flashlight to shine a bright light down the vent pipe to look for further blockage you can reach. If you can see but can't reach, run a plumber's snake down the vent pipe. To continue, feed the end of a garden hose down the vent and have someone on the ground turn on the water.

Do drain pipes need to be vented? ›

Without getting too far into building science, a general plumbing rule of thumb is that every drain needs a trap, and every trap needs a vent. All those traps and drains are designed to prevent sewer gas from entering your home.

What happens when plumbing vent is clogged? ›

When your plumbing vent pipe is clogged, you put yourself and your loved ones at risk. You'll likely know it's clogged if there's a gurgling sink or foul odors inside your house. Left unchecked, sewer gasses can seep into your home to cause sickness or even lead to explosions.

How does a plumber vent a waste pipe? ›

Common Types of Plumbing Vents Pipes

It's a vertical pipe attached to your drain line. Because no water runs through it, it vents from the roof. Common vent: Use a common vent between two fixtures installed on opposite sides of a wall, like back-to-back sinks. They're connected to the stack with a sanitary cross.

How often do plumbing vents need to be cleaned? ›

In general, you should clean your vents at least once every two to five years. However, if you notice any of these symptoms and conditions of dirty air vents, it's best to start cleaning immediately: Excessive dust, debris, or particles being released from the supply vents. Visible mold growth inside your ductwork.

How do you unclog a vent pipe? ›

How to Clear a Clogged Plumbing Vent | This Old House - YouTube

How much does it cost to clean a plumbing vent? ›

Plumbing Vent Cleaning Cost

Plumbing vent cleaning costs $100 to $200 on average. Signs stacks aren't venting include bad odors, slow drainage, gurgling noises, or when someone flushes a sink and another sink makes a noise. Using an open cover or screen at the end of the vent pipe prevents debris from clogging.

Why do my drains gurgle? ›

So, what's causing your gurgling pipes? Gurgling pipes are a sign of either a clogged drain line or a clogged vent pipe. Obstacles can block water or air from freely flowing through your pipes. This results in trapped air or gas bubbles, which is the gurgling sound you may hear.

Where should a plumbing vent be located? ›

Vent pipes must be installed so they stay dry. This means that they should emerge from the top of the drainpipe, either straight vertically or at no less than a 45-degree angle from horizontal, so that water cannot back up into them.

Why does my house smell like sewer at night? ›

Why does my house smell like sewer at night? Some of the top reasons for sewer smell at night may be due to a broken drainage pipe, a cracked vent stack, a clog, a problem with your septic tank, and many more.

How does a drain vent work? ›

Vents. Plumbing vents are pipes that extend from the waste pipes to the outside of the building, often going through the roof. The vent pipes allow the sewer gases to escape to the outside, rather than being released inside the house. The vent pipes also allow oxygen into the waste pipes.

Do all houses have a plumbing vent? ›

How Do I Get Them Installed? As part of the new regulations in compliance with building codes, you are required to have a plumbing vent and a trap for every fixture in the home that requires plumbing, for example, toilets, bathtubs or sinks.

Do plumbing vents have to go through the roof? ›

Although the plumbing vent that terminates in outside air usually runs through the roof, the IRC allows other options—such as running up an outside wall—as long as the termination is away from doors, operable windows, any soffit vents, and a minimum of ten feet above ground.

What causes negative pressure in plumbing? ›

A negative pressure occurs in a drainage stack as water rapidly flows downward, drawing air into itself (entrainment). If the sheet of water flows past an unvented branch connecting to the stack, a negative pressure will also be produced in the branch, affecting any trap seals in the branch.

Why does my bathroom sink gurgle when I shower? ›

Gurgling is caused when something is preventing water or air from flowing through your drains. As the water slowly travels through your drains, air bubbles begin to form and create a gurgling sound. Whether it's your sink, toilet or shower, even floor drains all can make that gurgling sound.

What is the difference between drain waste and vent? ›

Drain refers to water produced at fixtures such as sinks, and showers; waste refers to water from toilets. As the water runs down, proper venting is required to allow water to flow freely, and avoid a vacuum from being created.

Can a plumbing vent go out a wall? ›

You can pass the vent through a wall instead of through the roof, but it must still rise over the roof.

Does a plumbing vent pipe have to be straight? ›

Do Plumbing Vent Pipes Need to be Straight? Plumbing vents need to be straight on the vertical. This is necessary to avoid any vapor locks from occurring. When there is a bend in the vent pipe, moisture accumulates and is trapped.

Will a toilet flush without a vent? ›

Yes, every toilet needs a vent pipe to work well. Without it, your toilet could not get rid of waste and debris. The toilet needs venting to balance the atmospheric pressure, enable the flush system, and prevent awkward smells.

Does a shower drain have to be vented? ›

Vent Pipe Requirements for Showers

It's easy to forget, but it's a vital and required part of any plumbing fixture drain. The vent pipes remove sewer gases while allowing air into the system to help the water drain. Without a vent, your shower won't drain correctly.

Do old houses have plumbing vents? ›

Old houses frequently aren't vented properly, but it's hard to tell how bad it is until the ceilings and walls are out. In modern plumbing, vents carry exhaust and sewer gases up and out of the house. Vents also allow fixtures to drain properly -- sort of like putting two holes in a can to get it to pour freely.

Can a toilet and shower share the same vent? ›

So yes the shower can also be vented by the wet vent along with the toilet. There is one major stipulation when wet venting multiple fixtures when a toilet is one of them: the toilet must be the last fixture connected to the wet vent.

Why does downstairs toilet gurgles 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.

How do you vent a toilet drain pipe? ›

How To Vent & Plumb a Toilet (in 2022) - YouTube

How many drain vents should a house have? ›

At least one main vent stack is required for every building that has plumbing when connecting separately to the sewer for the building or its septic tank. The stack has to run the most direct route through open air or be ventilated to extend to open air.

Do bathtubs need a vent pipe? ›

All bathtubs need to have vents in order to operate properly. Bathtubs that do not have vents could release strong smelling and potentially dangerous fumes. Bathtubs without vents also drain slowly and may make bubbling or gurgling noises.

How do you properly vent a shower? ›

Bathroom Shower Vent - Installation Tips - YouTube

What happens when an air admittance valve fails? ›

Failure to bring air back into the pipes can result in a vacuum (causing slow draining and gurgling), or even the siphoning of water out of traps (allowing sewer gases to enter the home through drain openings).

How long does an air admittance valve last? ›

AAV's are certified to reliably. However anything mechanical can and will fail. Some manufacturers claim they're good for 500,000 uses (approximately 30 years of use).

Where should I place my air admittance valve? ›

Air Admittance Valves must be installed on a soil pipe at least 200mm above the highest water entry point on the system – that is the highest point that water can normally reach in a soil pipe.

Do plumbing vents have to go through the roof? ›

Although the plumbing vent that terminates in outside air usually runs through the roof, the IRC allows other options—such as running up an outside wall—as long as the termination is away from doors, operable windows, any soffit vents, and a minimum of ten feet above ground.

Can a plumbing vent go through a wall? ›

You can pass the vent through a wall instead of through the roof, but it must still rise over the roof.

Where is the plumbing vent located? ›

Plumbing vent pipes are located on roofs, away from windows or air conditioning units, so that the fumes can easily dissipate.


1. How to Clear a Clogged Plumbing Vent | This Old House
(This Old House)
2. How to identify and correct a venting problem with a shower drain.
(Bearman the Handyman)
3. Why Do I Need Vents in My Plumbing System The Importance of Air Vent Pipes
(The Fixer)
4. How to Determine if you Have a Broken Sewer Pipe
(Doug Smith)
5. How do I know if my plumbing vent is clogged?
(Ask About MOVIES)
6. How to Diagnose a Gurgling Sink | Ask This Old House
(This Old House)

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