Why Does My Toilet Keep Blocking?

One blocked toilet is bad luck. A toilet that blocks every few weeks is a symptom. Plunging it clear again fixes the day, but the cause is still there, and it usually gets worse.

The good news is that a repeat blockage leaves clues. A few questions will narrow it down before anyone lifts a manhole cover.

First question: one toilet, or the whole house?

This is the most useful thing to work out, because it tells you where to look.

Only one toilet blocks, and the sinks, shower and other toilets drain normally: the problem is almost always in that toilet or the short pipe just beyond it.

Several fixtures are slow, the toilet gurgles when the shower or washing machine drains, or water rises in the shower when you flush: the blockage is further down, in the line that everything shares. Another sign is the overflow relief gully outside, the grated drain near the house, overflowing or smelling. That is a sewer line problem, and plunging the toilet will not fix it.

Cause 1: what goes down it

Toilets are designed for waste and toilet paper, and nothing else. The most common cause of repeat blockages we see is something else going down, a little at a time.

Wipes. Baby wipes, make-up wipes and wipes sold as “flushable” do not break down the way toilet paper does. They catch on pipe joints and rough spots, and each one makes the next more likely to stick.

Too much paper for the flush. Modern dual-flush toilets use much less water per flush than older single-flush models. They work well, but a large wad of paper on a half flush may not make it far enough down the pipe. Use the full flush when there is a lot of paper, or flush twice.

Other things that do not belong: cotton buds, dental floss, sanitary products, paper towel, tissues, cooking fat and kitty litter. Tissues and paper towel are made to stay strong when wet, which is exactly the problem.

If you have young children, or guests who may not know the rules, a small bin in the bathroom and a quiet word solves a lot of callouts.

Cause 2: something stuck in the pan

The toilet pan has a curved passage, called the trap, built into the porcelain. A small toy, a toothbrush, a bottle lid or a hairclip can lodge in that bend without blocking it completely. Water still gets past, but paper catches on the object, and the toilet blocks again and again.

The giveaway is a toilet that blocks often, clears easily with a plunger, and then blocks again within days or weeks, while every other drain in the house is fine. Plunging tends to push the object back and forth rather than out.

Getting it out can mean lifting the pan off the floor to reach it from behind. That is a job for a plumber, because the pan has to be reset and resealed to the drain afterwards.

Cause 3: a problem in the sewer line

If the problem is further down, the toilet is just the first fixture to show it, because it sends the most solid waste into the line.

Tree roots are the classic cause in older Sydney suburbs. Many homes still drain through clay pipes with joints that roots can get into. The roots form a net inside the pipe, paper catches on it, and the line slowly closes up. Our guide to tree roots in drains covers the signs.

A dip or displaced joint. Ground movement, reactive clay soil and old age can make a section of pipe sag or a joint shift. Waste settles in the low point or catches on the lip of the joint.

Build-up of fat, scale and debris narrows the pipe over years, so each flush has less room to get through.

These do not go away with a plunger. The line needs clearing properly, usually with a high-pressure jetter, and a CCTV drain camera shows what caused it so the fix matches the fault.

Cause 4: venting and installation

Less often, the toilet or its drain was installed in a way that makes blockages likely. A drain pipe without enough fall does not carry waste away quickly. A blocked or missing vent can starve the system of air, so flushes are weak and the toilet gurgles.

This is more common after a renovation that moved the toilet, or in extensions where the drainage was added later. If a toilet has blocked regularly since it was installed, this is worth considering.

Clearing it safely

Stop flushing. If the bowl is full, another flush will overflow it. Take the lid off the cistern and hold the flapper closed, or turn off the isolation valve behind the toilet.

Use the right plunger. A toilet plunger has a flange, an extra rubber sleeve that fits into the outlet at the bottom of the bowl. Push down gently to make a seal, then work it firmly up and down. Make sure there is enough water in the bowl to cover the cup.

Skip the chemicals. Drain cleaners rarely shift a toilet blockage, can damage older pipes and seals, and leave caustic water in the bowl.

Do not force things. A wire coat hanger can scratch the porcelain and push an object further in. If a plunger does not clear it after a few minutes, stop there.

When to call a plumber

Call a licensed plumber if the toilet blocks more than once in a couple of months, if other fixtures are slow or gurgling, if the overflow relief gully outside has overflowed, or if you can smell sewage outside. Sewage in the yard is a health risk, so keep children and pets away from it.

A repeat blockage needs its cause found, not just cleared again. That usually means clearing the line and then putting a camera through it, so you know whether you are dealing with an object, roots, or a damaged pipe. If you want the wider picture first, our guide to why drains block covers the rest of the house.

FAQs

Are flushable wipes safe to flush?

No. Wipes sold as flushable do not break down the way toilet paper does. They snag on joints, roots and rough pipe walls and build up into blockages. Put them in the bin.

Should I use a chemical drain cleaner on a blocked toilet?

No. Chemical cleaners rarely shift a toilet blockage, they can damage older pipes and seals, and they leave caustic water in the bowl for whoever clears it next. A plunger, or a plumber, is the better option.

Why does my toilet gurgle when I run the shower or washing machine?

Gurgling at the toilet when other fixtures drain usually means air is being pulled through the toilet’s water seal. That points to a partial blockage further down the line or a blocked vent, and it is worth having checked before it becomes a full blockage.