What Happens When You Flush Down the Toilet?

Written by

Paulk Webb


Freddie J. Hagopian

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what happens when you flush down the toilet

You likely asked yourself at least once: where does poop go when you flush? What happens to all those solid and liquid waste that go down the drain?

What happens when you flush down the toilet is that all those wastes will travel down your drain pipes and will eventually reach the sewer system.

The sewage will then traverse the underground sewer line until it reaches the waste treatment plant in your locality. Here, it undergoes a series of treatments to prepare itself for release back to mother nature.

Read further to better understand the journey your poop, as well as other wastes, takes as you flush them down the toilet bowl.

Where Does Waste Go When You Flush the Toilet?


Basically, wastes will be pushed down through several drains and pipes whenever you flush your toilet. Gravity and pressure from flushing enables all forms of waste to move away from your home.

As the waste travels through your home’s drain system, it will eventually meet your local sewage lines. All wastes within your neighborhood will be collected — eventually reaching the nearest wastewater treatment facility.

Here, the sewer water undergoes a series of processes that will separate sludge and debris from the water. This also entails eliminating any sickness-causing germs from the treated water or ‘effluent.’

Most of the sludge and solids are converted into fertilizers and fuel. Meanwhile, the treated and disinfected water will be released back to waterways, ready for another cycle of consumption and treatment.

But it is worth mentioning that not all waste water goes down the drain when you flush your toilet. A study has shown how much waste scatters into the air upon flushing.

As it goes down into the sewer, some tiny droplets and particles of toilet water (ranging from tenths of microns to a millimeter in size) are spewed out from the bowl when you flush the toilet with the lid open.

Although miniscule amounts of the flushed water gets released into the air while flushing, the majority will undergo treatment and return back to the environment for another cycle.

The Sewage Treatment Process

Sewage or wastewater treatment is a multi-step process that ensures used water is free from debris, waste, and hazardous chemicals before its discharge into the environment.

Here’s what happens to sewage as it is being cleaned and treated in facilities:

1. Inlet Works


After you flush and upon arrival at the facility, the sewage is screened in the inlet process. Large debris of solids are separated from the rest of the liquid waste to prevent problems in the next steps.

Things that shouldn’t be flushed in the toilet like jewelry, toys, cleaning wipes, diapers, as well as accumulation of oil and grease are filtered out in this stage.

2. Balance Tanks


To prevent overflow in the treatment plant, the screened sewage is held in special balance tanks first. This controls the flow to ensure quality and consistency of sewage treatment.

3. Bioreactor

The sewage may be visibly free from debris, since it’s already screened earlier. But it’s still filled with organic matters detrimental to bodies of water and the life around it.

For this reason, the treatment process makes use of bacteria that consume all the nitrogen, carbon, and phosphorus, effectively getting rid of these organic residues.

These bacterias are housed in oxygen-filled bioreactors that can support their reproduction and continuous consumption of the organic matter in the sewer.

4. Clarifiers


After getting rid of all the organic nutrients, the solids are separated from the remaining water in the special clarifiers.

These solids known as sludge or biosolids are drained, dried, and used as fertilizers.

Meanwhile, the remaining liquid is now the treated water called effluent. Despite this cleaning stage, it will still undergo processing and disinfection in the next couple of steps.

5. Filtration and Disinfection


To ensure the treated water is safe for discharge to the environment, another filtering stage is necessary.

Treatment plants use UV rays or chlorine to kill unwanted microorganisms that affect the quality of the treated water.

6. Testing

As a final step to the treatment process, the effluent goes through testing to ensure it adheres to strict standards of quality control.

The raw and nasty sewage water after treatment lasts about 1-2 days before it’s ready to return to the environment.

Amount and Cost of Sewerage Usage

Of course, we pay for these water treatment processes so that the facilities doing them can sustain their operations and continuously provide services for us residents.

The amount of sewerage usage for households is estimated to be 168 liters/person/day on average. The maximum usage is capped at 740 liters/day/person.

Shown below are the projections of cost, depending on the number of households members:

Average water usage per person per day No. of people in household Cost to process waste per day Total cost per year

168 liters/person/day

1 person 10 cents/day $36.5/year
2 people 20 cents/day $73/year
3 people 30 cents/day $109.5/year
4 people 40 cents/day $146/year
5 people 50 cents/day $182.5/year

As low as these prices are already, these charges can be further reduced by conserving water as well as taking good care of your drain pipes.

Less usage of water means less dirty water to clean and treat in the facility; while being mindful of things you flush down ensures lower risks of clogging and pipe damage. All these save you and your local treatment facility from additional charges.

Be Careful About What You Flush Down the Toilet


Flushing stuff down the toilet, accidentally or not, is harmful to your drain pipes as well as your local sewer system.

These debris or objects can accumulate in the pipes of the toilet and will cause clogging, which is basically the main cause of almost all toilet problems and eventual costly repairs.

Even worse, clogging can accumulate in the pipelines of your city’s sewer system, affecting not only your household but your whole neighborhood, as well.

Avoid flushing the following household items down the toilet:

  • Toilet paper (simultaneously and in large amounts)
  • Paper towels and wet wipes
  • Hygiene products like menstrual pads
  • Cotton balls and q-tips
  • Medicine
  • Jewelries
  • Toys and other plastic items

Basically, only human waste and, occasionally, toilet papers are safe for toilet flushing. Anything else, regardless of size and amount, will eventually cause serious problems.

What to Do When You Accidentally Flushed Something Down the Toilet?


If the item is still visible, you can fish it out gently.

For example, when you see a toy flushed down toilet but it is still reachable, you can wear rubber gloves and try to retrieve the item by hand.

If you don’t see the items anymore, try these methods to hopefully get the flushed item to resurface:

  • Plunger – plunge gently and hope that the suction can move and force the item to float back up.
  • Bent wire hanger – the bent part can be used to grab and pull the item up. Beware that this method risks completely lodging the object into the pipe or scratching your toilet’s porcelain surface.

If nothing floats back, you’ll need professional help. Plumbers can use special equipment to find and retrieve the item before it brings damage to your pipes.


Learning what happens when you flush down the toilet made us understand the cycle of consumption and treatment water goes through everyday.

As long as there are no clogging problems, the flow of toilet water through the drain and sewer system and into the treatment plant is systematic and cost-effective.

So, we can’t stress it enough: never flush plastic down the toilet, or any other foreign objects for that matter, to avoid household and community-level bathroom problems.

As much as we benefit from the waste treatment process, we are equally responsible for taking care of our toilet and its pipes.

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