5 signs of a blocked sewer drain

out of order blocked sewer

Who’d be a plumber? Bad enough all that back-breaking digging in dark, muddy places but did anyone ever warn them about a blocked sewer?

Unpleasant as it may sound, most plumbers actually spend a significant portion of their day clearing or repairing sewer pipe blockages. Sure, it pays the bills but there are certainly more pleasant ways for them to earn a buck.

We’ve spoken to a number of experienced, professional plumbers to get the real dirt on blocked sewers. We asked:

  • Why do we get blocked sewers in the first place?
  • What are the signs of a blocked sewer?
  • What can homeowners do to avoid blocked drainage pipes in the first place, or to clear a blocked sewer themselves?

Their answers have helped us identify 10 of the most common causes and 5 of the most common signs of a blocked sewer. This article also discusses the long term impacts a blocked sewer can have on a property and offers some tips to not only help you avoid a sewer line blockage at your place but to clear a blocked pipe yourself.

Finally, if the DIY remedies for clearing a blocked sewer fail, there is some advice about the sewer pipe repair alternatives commonly available today.

10 common Causes of sewer blockages

Let’s face it. Most of us have a love-hate relationship with the toilet. When it’s time to clean the bathroom, the toilet’s the least pleasant job on the list, but when you’re caught short out on the road, making it to the service station loo in the nick of time can sometimes be as gratifying as winning the lottery.

But as glorious as that gleaming white porcelain appears after we’re done scrubbing, it’s what’s happening beneath the throne that really matters. To be blunt, most sewer issues occur when inappropriate items are placed into toilets. Some people seem to view the toilet as a rubbish bin; fit for disposal of everything from documents to leftover grout and plaster.

In fact, the list of items our plumbers had found in sewer pipe blockages was so extensive, we created a downloadable sign for readers to print off to help remind toilet-users what can and can’t be flushed.

We’ve also narrowed their lists to identify the top 5 ‘Carelessness Culprits’. They are:

1. Nappies

2. Facial tissues and wipes (supposedly ‘flushable’)

3. Sanitary products and condoms.

4. Cleaning items (scrub pads, paper towels)

5. Dental floss and hair.

Add to that the inadvertent, more natural causes which include:

6. Tree root invasion

7. Natural deterioration of the pipe

8. Earth movement

9. Temperature extremes

10. Renovations or building works (on or near a property).

5 signs of a blocked sewer

Once sewer pipe blockages occur it’s very important that repairs are carried out reasonably quickly. But with pipes usually buried deep in the ground or under house slabs and driveways smaller blockages and leaks can often go unnoticed for months or even years.

There are, however, some signs astute homeowners can look for to get the heads up on sewer line blockages before it’s too late. The 5 most telling signs are:

Inside the home

  1. Slow, incomplete or cessation of flushing:

The most common sign of a sewer issue is when you push flush, only to watch the unpleasant concoction swirl up to the brim instead of unobtrusively draining away as it should. You hold your breath and pray suction will do its thing, and for the first dozen or so times (painfully slowly) it does. Problem solved? Not likely.

Recurrent blockages and slow-to-drain toilets are usually signs your sewer pipes need professional help. What may have started as a small, easy-to-budge blockage may well have led to a crack and then to complete breakage of the pipe. As dirt caves in through the break and matter continue to back up, flushing becomes inefficient and a cleanout, reline or replacement will be needed.

If you have multiple plumbing fixtures backing up at the same time it can be a sign of a complete sewer system clog and you should call a local professional to advise on the best repair strategy.

  1. Gurgling in pipes or back-filling into other outlets

If you can hear gurgling, rattling or shaking in pipes it means there is air in there and it’s causing pipes to not flow correctly. When someone flushes the toilet and gurgling can be heard (either in the bathroom or elsewhere, like the kitchen) it’s a sign the water supply is being impeded in some way. Even if the issues are not yet severe, a CCTV pipe inspection is recommended to assess whether there might be a (now) small blockage or break which is leading to pipe malfunction. If there is, and it can be cleared and possibly relined using CIPP relining homeowners can avoid the possibility of a small issue becoming a major headache.

  1. Mould or mildew on non-shower walls

Mould and mildew can travel up walls if there is moisture in the ground from either water or waste. If sewer pipes are leaking underground, much of the smell may be absorbed by the soil but the moisture can still sit under foundations and make their way up walls leaving little evidence other than mould or mildew.

In the yard

  1. Areas of lush, green grass, damp soil, and ponding or wet paths, brickwork or concrete

If there’s an area of grass or garden that’s really thriving when everything else is struggling, think hard about why. If you can’t come up with anything more than good luck or a green thumb, then think again.

Likewise, think a little more deeply when you see wet patches out in the yard and dismiss them as poor drainage or a brief shower you must have missed. Get up close and personal and check whether there is also an odour. It may not be as strong as raw sewage because of the soil’s ability to dilute and absorb the bacteria, but it will still be noticeable.


  1. Foul odour

If there is an unpleasant smell in your bathroom, house or yard which you’ve never noticed before, it’s always important to investigate. Check whether it’s near a sewer line on your house plans. Depending on the type of damage, it is possible for a broken pipe to be leaking sewage without blocking your toilet or leaving visual signs of moisture. And remember that a leaking sewer pipe presents just as much potential danger to your home’s structure as leaking water pipes so don’t lull yourself into a false security just because the smell only ‘comes and goes’.

impacts of a blocked sewer

Leaking or blocked sewers are not only highly inconvenient they can result in health concerns and, if left unattended, can undermine a home’s foundations. As blockages increase in size and become tougher over time they can put pressure on the whole pipe system. This causes cracks, splits and ruptures which can lead to a complete sewer system failure.

How to avoid sewer pipe blockages

The following steps will give you the best chance of avoiding sewer troubles.

1. Only put human waste and toilet paper into your toilet.

Ensuring the items listed above never enter your sewer system is the first step toward avoiding sewer pipe blockages.

2. Educate everyone who lives in the home on correct usage

Educating others who live in the home about what can and can’t go into the toilet is the next step. This may include erecting signage if you feel reminders will help.

3. Carry out regular sewer pipe maintenance

A monthly maintenance program can ensure small blockages are cleared and pipes function as they should. You can read about maintaining healthy pipes here.

You should also consider having a CCTV pipe inspection of your sewer pipes every year or two, to check whether there has been any tree root invasion, pipe deterioration or cracking as a result of earth movement.

More information about how to avoid blocked sewer pipes can be found here.

How to clear a sewer pipe blockage yourself

Before spending money on professionals, many people want to try to clear blockages themselves. This is perfectly understandable, and they can often have some success, particularly if the blockage is near the top of the pipe.

If the blockages are recurrent or deeper in the pipe, however, a professional will need to be called. In the meantime our plumbers have shared some of the most commonly used DIY tricks for clearing blockages in pipes and drains. They are:

  • Hot water and dishwashing liquid
  • Vinegar, baking soda and salt
  • A plunger
  • Plastic or cling wrap on the toilet bowl
  • A wire hook
  • Lye
  • Chemical cleaners.

Finding the best sewer pipe repair option in your local area

If you want to know more about repair options, you can read our article, ‘Sewer pipe relining vs replacement’. The article includes a downloadable table which compares all the options for sewer pipe repair. Alternately you can contact us for advice on how to find a sewer pipe repair professional near you.



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