Key takeaways
- ✓ Only toilet paper and human waste should ever be flushed — wet wipes, paper towels, cotton balls and dental floss are common causes of clogs and sewer overflows.
- ✓ Older low-flow toilets from the 1990s often lack the flushing pressure to clear the trap and drain, causing frequent clogs.
- ✓ Most trap blockages can be cleared with a plunger, but blocked roof vents and sewer line problems need a professional.
- ✓ Tree roots, wet wipes and built-up fats are leading causes of sewer line blockages and wastewater overflows (Sydney Water).
- ✓ Frequent clogging across multiple drains is a warning sign of a sewer line problem — and an overflow of raw sewage is a health hazard that needs professional clean-up.
Why toilets clog — and why it matters
The toilet is one of the hardest-working fixtures in your home, and when it blocks up, things get stressful and messy fast. A bad enough backup means raw sewage on your bathroom floor — a genuine health hazard, not just a nuisance. Understanding what actually causes toilet clogs is the best way to prevent the next one. Here are the five most common culprits.
1. A first-generation low-flow toilet
Many older low-flow toilets simply lack the flushing pressure to clear the internal trap and drain, which leads to frequent clogs. Check the back of your toilet for a stamped manufacture date — if it dates from the mid-1990s, you may have a first-generation low-flow model. That doesn't mean you need to rush out and replace it: you can cut clogs dramatically by using less toilet paper per flush and keeping anything non-flushable well away from it.
2. Flushing non-flushable items
Your toilet is designed to handle two things: human waste and toilet paper, which breaks down quickly in water. Almost everything else causes trouble. Paper towels and tissues don't dissolve the way toilet paper does, and items like wet wipes — even ones labelled "flushable" — cotton balls and dental floss restrict drainage and cause repeat backups. Talk with your household about what can and can't be flushed. If you have young kids, a simple list near the toilet helps, and a decent-sized bin in the bathroom builds the habit of binning hard-to-flush items instead of flushing them.
3. A clogged toilet trap
The trap is the curved section of pipe built into the base of your toilet. It holds a pocket of water that stops sewer gases rising up into your home. Toilet paper, paper towels and non-flushable items can lodge in this bend and block it, backing the toilet up. The good news: a trap blockage is the one you can usually fix yourself — a firm session with a plunger will loosen most trap clogs. To keep the trap clear, go easy on the toilet paper and keep everything else out of the bowl.
4. A blocked plumbing vent
Modern plumbing systems use a roof vent to draw fresh air into the pipes, which maintains healthy flushing pressure. Over time, that vent can block up with leaves, sticks or a bird's nest. When it does, drain flow and flushing pressure drop across the house and clogs become a regular event. Vent blockages are hard to spot and awkward to reach, so this is a job for a professional with the right tools.
5. Problems in the sewer line
If your toilet and other drains keep clogging, the problem is probably further down — in the sewer line itself. Sewer blockages build up from accumulated waste and non-flushable items, and tree roots can crack or puncture the pipe, letting soil and debris in. Wet wipes, fats and tree roots are among the most common causes of wastewater blockages and overflows. A failing sewer line causes serious problems inside and outside the home, and overflowing wastewater carries bacteria and viruses that can make your family sick — so keep children and pets away from any overflow and call in the professionals. If it's already happened, our guide to sewage backup health risks explains what you're dealing with.
Need a hand in Sydney or Regional NSW?
If a blocked toilet has turned into an overflow or sewage backup, don't risk cleaning it up yourself. One Prime Solutions provides professional sewage clean-up — removal, cleaning and full sanitisation of the affected area — responding 24/7 across Greater Sydney & Regional NSW. Call 1300 774 631 and leave the mess to us.
Frequently asked questions
Are flushable wipes actually safe to flush?
No. Even wipes labelled flushable don't break down the way toilet paper does. They restrict drainage, cause repeat toilet backups and are one of the most common causes of blocked sewer lines and wastewater overflows. Bin them instead.
Can I fix a clogged toilet myself?
Often, yes — if the blockage is in the toilet's trap, a firm session with a plunger will usually clear it. But if clogs keep coming back, or multiple drains in the house are affected, the problem is likely a blocked vent or a sewer line issue, and that needs a professional.
How do I know if my sewer line is the problem?
The tell-tale sign is frequent clogging in the toilet and other drains at the same time. Sewer lines block up from accumulated waste and non-flushable items, and tree roots can crack the pipe and let debris in. A plumber can inspect the line with a drain camera to confirm.
Is a sewage overflow dangerous?
Yes. Overflowing wastewater carries bacteria and viruses that can cause gastroenteritis and other illness, so keep children and pets well away from affected areas. Saturated porous materials often need to be discarded, and the area needs proper professional cleaning and sanitisation before it's safe again.
Sources & further reading
This article is general information, not medical or legal advice. Last reviewed 14 November 2018 by the One Prime Solutions team.