Science Experiment: Flushable or Not Flushable?

This science project is great for all middle school students to learn what is good and bad for our sewer system!

Setting the Scene

At first glance, the toilet may seem like a most convenient place to dispose of things that you want to be out of sight and out of mind. Just push down on the handle, and stuff disappears. But does it really disappear? A toilet is for organic body waste and toilet paper only. Everything else should go into the garbage. Some of the stuff you might be tempted to flush might actually clog up your pipes and cost your family a whole lot of money to repair, or it might cause damage to the wastewater treatment system itself.

Stories abound of people who flush paper towels or wrappers of various kinds down the toilet and then have to suffer the vile consequences. Materials that do not biodegrade completely eventually clog the pipes and cause a home’s plumbing to back up, maybe filling the sinks or the floors with stinky unprocessed waste from the sewer pipes. Sometimes the leaking, stopped-up pipes can even leak through floors, destroying the ceiling and resulting in a rainstorm of raw sewage.

The Basic Science: Biodegradability

Materials that are biodegradable break down into their basic component parts and return to nature. Leaves, for example, grow in the spring, fall to the ground in the autumn, and biodegrade in the winter. By springtime, many of their nutrients have returned to the earth for plants to use during the next year. Most plastics, on the other hand, take centuries to degrade and return to the state of their basic elements.

Most papers biodegrade, but over varying time spans. For the most part, paper is made of crushed wood fibers that are then pressed into sheets. (If you look at a sheet of paper through a microscope, you will clearly see the wood fibers.) Some papers, however, are made to be strong and to last, while others, such as toilet paper, are made to break down very quickly in the presence of moisture.

In this science project, you will measure the speed with which common products break down and begin the process of decomposition. From these observations, you will be able to make suggestions about materials that should or should not be flushed down the toilet.


One-quart jars, such as Mason jars or empty mayonnaise jars, filled with tap water (You will need one jar for each material to be tested)

Materials that you may want to test:

  • single-ply toilet paper
  • double-ply toilet paper
  • various brands of toilet paper
  • flushable wipes
  • non-flushable baby diaper wipes
  • tissue
  • pieces of newspaper
  • paper towels
  • coated paper, such as wax paper or wrapping paper from a fast-food sandwich
  • wrappers from personal hygiene products that may wind up in the toilet
  • Any other products you want to test

Be sure to use jars for this experiment and not your toilet. The non-degradable materials could clog your toilet and cause significant damage to your home.


  1. Fill each jar with tap water and put in one piece of sample material.
  2. Shake the jar one or two times each time to agitate the contents. Take care to shake each jar with roughly the same vigor and for roughly the same time.
  3. Observe, draw, and describe the changes in the materials over a span of time. Ideally, you will be able to make these observations over a period of 2 to 6 weeks.
  4. Create graphs of the changes in the materials over time.
  5. Make recommendations to your class and your community about materials people could or should not flush down the toilet.

Additional Ideas

  • Research the process of wastewater treatment. What substances do treatment plants effectively treat, and what substances (perhaps like oils and solvents) may damage the wastewater treatment system itself?
  • Research plumbing pipe materials and make a recommendation to a new homeowner about how to extend the life of the plumbing pipes as long as possible.
  • Create posters that communicate to people what should and should not go into a toilet.
  • Interview a plumber about “horror stories” he or she has seen when people have flushed non-degradable materials down the toilet for extended periods.

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