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How to Tell If Your Main Sewer Line is Blocked

sewer line blockage

A Blocked Main Sewer Line is a Hazard

The sewer line is arguably the most important part of your home’s plumbing network. The toilet, shower, kitchen sink, and floor drains all flow towards and connect with the main sewer line, which removes wastewater from your property and to the council-managed sewers.

So, if this line has a clog, there’s potential for it to affect all of your plumbing. Completely blocked sewer lines can wreak havoc on your house if not addressed in a timely manner.

The good news is that our useful guide highlights the warning signs and causes of a blocked sewer line along with the best solutions for getting your house back on track.

Here’s what you need to know about a blocked sewer line:

Signs of a Blocked Sewer Line

Blocked pipes and drains are commonplace. It’s almost guaranteed that you will experience one at some point in time, to some degree.

Wastewater is not only disgusting but also dangerous. That’s why a blocked sewer drain must be addressed immediately.

So, before a clog gets out of hand, take action if you detect any of these warning signs:

Gurgling Sounds

A gurgling sound coming from the drain indicates that something is stopping air from escaping. When water is flowing, air should freely move through the pipe.

A partial obstruction will inhibit the air, which creates the gurgle. Gurgling sounds may seem commonplace, but they’re not supposed to be present at all. Instead, they indicate a partial blockage that could worsen over time.

bad smell in drain

Foul Smells

A foul smell emanating from a drain suggests one of two things: A clogged sewer line could be stopping excrement from washing away, and it remains there, sitting in your drain. Or, the smell could come from bacteria that feed on solid waste and produce a foul-smelling hydrogen sulphide gas. Neither is desirable, and both are signs of blockage in your sewage system.

Backed Up Drains

If water is slow draining or won’t drain at all and starts coming back up from within the pipe, you have a major blockage. This would suggest that the sewer system is completely blocked, and it’s not advised that you use any plumbing until it’s fixed, as you will only be making it worse.

The last thing you need is the foul smelling wastewater and hydrogen sulphide gas-producing bacteria coming out of the pipes and desecrating your home. Exposure to wastewater can lead to gastroenteritis (diarrhoea or vomiting), among other ailments.

A main sewer line clog can also have a negative effect on multiple plumbing fixtures.

Water Pooling or a Sagging lawn

Subsidence is the word for when a structure starts sinking into the ground. This is caused when soil shrinks or expands as a result of excessive water. You certainly don’t want this to happen, but water pooling on the property or visible sagging could indicate flooding from a blocked sewer pipe or broken drain.

Of course, you will likely uncover other signs beforehand, but this one should confirm any lingering doubts.

sewer line blockage

What Blocks Sewer Systems?

There are many causes of blocked sewer lines, some are contributed by occupants while others are out of your control. Here are the main culprits:


So many things contribute to blocked drains, and most are a direct result of what you flush or wash down the sink. Cooking oil, food grease, coffee grounds, wet wipes, hair, cat litter, and tampons are the most common causes of a blocked sewer line. Throw these items in the waste bin. You should only be flushing the three Ps – paper, pee and poo.

Tree Roots

Tree roots seek out moisture, so it’s not uncommon for them to aim directly for your plumbing. Tree roots put pressure on the pipes until they crack, and the roots push through becoming a blockage. You will need to call a plumber to rectify this one. Options include relining the pipe or replacing the damaged section.

Broken/Collapsed Pipe

Corrosion, ageing, tree roots and shifting soil can cause a damaged pipe that ultimately cracks, breaks, and lets in soil or roots. This is guaranteed to cause a blockage and is more common for an old pipe than a new one. An older house will likely have pipes made from steel, iron or clay. These materials have since been phased out, replaced by copper and PVC. This is because steel and iron are susceptible to rust, and clay pipes are brittle.

Sagging Pipe

Loose or shifting soil and tree roots can cause a pipe to sag or belly. This creates a low spot that interferes with the flow of wastewater. In addition, sediment and waste can build up in this sag, causing significant issues within the main sewer line. There’s not much to be done about tree roots concealed underground, but making sure soil is adequately compacted before installation reduces the risks of a sagging pipe.

tree roots blockage

How to Unblock Your Sewage System

The difficulty in accessing the sewer line depends on its location and the age of the plumbing. Many of the techniques used to clear a regular residential drain are ineffective due to the depth and vast expanse of the sewer line. However, some steps prove successful and are worth trying before calling in a plumber.


Hearing about prevention won’t do you any favours if you’re already dealing with a blockage, but it could help reduce the risks of it occurring again. Keep food scraps, oils, grease and coffee grounds out of the drain and only flush the three Ps.

Liquid Drain Cleaner

A drain cleaner may be effective and is the least labour-intensive method. However, chemical cleaners are not environmentally friendly and can even damage your pipes. This is why we have a great recipe for an all-natural, homemade drain cleaner that you can make with items in the pantry.

sewer cleanout caps

Sewer Clean Out

Occupants of modern homes may be aware of white capped pipework located outdoors and protruding from several parts of the property. These are called sewer cleanouts and connect to the main sewer line to easily remove blockages.

By code, there should be an access point at either end of the property. You can unscrew a cap and use a suitable tool to dislodge a blockage yourself. Drain snakes, hydro jetters and drain augers are available at hire yards and can save you money by doing the clearing DIY (assuming you’re capable and the blockage is caused by debris and not a broken pipe).

However, sewer clean outs have only been code for a few decades. So, older homes will not have this easy access.

Call a Professional Plumber

Calling a plumbing expert is the easiest way to address the problem with your sewer line and is the most likely solution for providing a long-lasting fix for the main drain.

A plumber will typically start by using a CCTV camera directed through a sewer line to pinpoint the exact location of the drainage issue and receive a visual indication of the blockage – tree roots, waste, broken pipe, etc.

A plumber will carry a hydro jet cleaner or drain auger that can clear out a blockage, then reline the pipe or replace a damaged section as required. Calling a plumbing expert is not the cheapest solution, but it is the most effective, as they can do whatever it takes to keep wastewater flowing to the sewer mains.

Are you looking for an expert plumber? Mr Emergency is available 24/7 for all plumbing work, including clogged lines and scheduled maintenance. We offer the services and possess the equipment to get your kitchen, bathroom, toilets, and sewage drains in order and keep water flowing for the long run.

Please note: This information is provided for advice purposes only. Regulations differ from state to state, so please consult your local authorities or an industry professional before proceeding with any work. See our Terms & Conditions here.

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