Dental floss does not break down in septic tanks and will clog your system

Dental floss is one of the most common items that damage septic tanks, even though many people flush it without thinking twice. Unlike toilet paper, which is designed to dissolve quickly in water, floss is made from nylon or similar synthetic materials that resist breakdown. When you flush floss, it winds around the impeller in your pump tank or tangles with other debris, creating blockages that can cost hundreds or thousands of dollars to clear.

The problem gets worse over time. A single strand of floss may not cause when ready trouble, but floss accumulates in your tank and combines with hair, grease, and other non-degradable items. This tangled mass can prevent your pump from working, back sewage up into your home, or damage the pump itself when a plumber has to disassemble it to remove the clog.

Your septic tank relies on bacteria to break down solid waste. Floss cannot be broken down by bacteria because it is not organic material. It straightforward sits in your tank, taking up space and creating hazards for the mechanical parts that keep your system running.

Key Takeaways

  • Dental floss is made from synthetic materials that do not decompose in septic tanks, no matter how long it sits there.
  • Floss tangles around pump impellers and combines with hair and grease to form blockages that require professional removal.
  • The cost to clear a floss-related clog typically ranges from $300 to $1,500 depending on how deep the blockage is and whether your pump needs repair.
  • Throwing floss in the trash is the only safe disposal method; no type of floss is safe to flush, including biodegradable brands.
  • Other items that seem harmless—hair, dental wipes, paper towels, and "flushable" wipes—cause the same damage and should also go in the trash.

Why synthetic materials survive in septic tanks

Septic tanks work through a biological process. Bacteria consume organic solids and break them down into liquids and gases that can drain safely into your drain field. This process takes weeks to months, but it works because the bacteria can digest materials like food waste, human waste, and toilet paper.

Floss is made from nylon, Teflon, or similar plastics. Bacteria cannot digest plastic. The floss will remain intact in your tank for years, accumulating and creating a physical obstruction rather than being processed like other waste. Even floss marketed as "biodegradable" or "eco-friendly" does not break down in the anaerobic (oxygen-free) environment of a septic tank, where decomposition happens much more slowly than in soil or compost.

The same principle applies to other synthetic items people commonly flush: dental wipes, makeup remover pads, and even some brands of "flushable" wipes. These products are designed to break apart in water, not to decompose biologically. They will clog your system just as easily as floss.

How floss creates blockages in your tank and drain field

If your septic system has a pump tank (which most modern systems do), floss is especially dangerous. The pump has a rotating impeller that moves liquid from the tank to your drain field. Floss wraps around this impeller like thread around a spool. Once wrapped, it prevents the pump from turning, and the motor burns out trying to force it.

Even in gravity-fed systems without a pump, floss accumulates in the tank and eventually blocks the outlet pipe that allows treated liquid to flow into the drain field. When the outlet is blocked, sewage backs up into your home through drains and toilets.

Hair causes the same problem. A single strand of hair is harmless, but hair accumulates in your tank over months and years, tangling with floss, grease, and other debris. The combination creates a mat that nothing can pass through. Plumbers call this a "clog ball," and removing it often means pumping out the entire tank and disassembling the pump to pull out the blockage by hand.

The cost of floss-related septic damage

A routine septic tank pumping costs $300 to $500 and should happen every three to five years. If floss has clogged your pump or outlet pipe, you are paying for an emergency service call, which typically costs $500 to $1,500 depending on how difficult the blockage is to reach and remove.

If the pump impeller is damaged by floss wrapping around it, you may need to replace the pump entirely. A new pump costs $1,500 to $3,000 installed. If floss has caused a backup that has already damaged your drain field, replacement costs can exceed $10,000.

These costs are entirely preventable. Throwing floss in the trash costs nothing and eliminates the risk entirely.

What to do with floss instead of flushing it

The only safe way to dispose of floss is to throw it in the trash. Wrap it around your finger or a small piece of toilet paper so it does not unravel in the garbage, then place it in your waste bin. This takes the same amount of time as flushing it, but it protects your septic system.

If you are concerned about floss in a landfill, consider switching to a water flosser (a handheld device that sprays water between teeth) or wooden floss picks, which can be composted. These alternatives eliminate the problem at the source rather than trying to dispose of traditional floss safely.

Some people use floss picks—small plastic handles with floss attached—thinking they are safer. They are not. The floss itself is still synthetic and will still clog your tank. Throw the entire pick in the trash.

Other items that damage septic systems the same way floss does

Floss is not alone. Many common bathroom and kitchen items will clog your septic system because they do not decompose:

  • Hair: Accumulates in the tank and tangles with other debris. Use a drain strainer in your shower and sink to catch hair before it enters the system.
  • Paper towels and napkins: Unlike toilet paper, these are not designed to dissolve quickly. Throw them in the trash.
  • "Flushable" wipes: These are marketed as safe to flush but do not break down in septic tanks. Throw them in the trash regardless of what the package says.
  • Dental wipes and makeup remover pads: These are small and seem harmless but accumulate and clog just like floss.
  • Feminine hygiene products: These should never be flushed. They do not decompose and cause severe blockages.
  • Cotton swabs and cotton balls: These do not break down and will clog your system.
  • Grease and cooking oil: These solidify in your tank and drain field, creating blockages and killing the bacteria that process waste.

The rule is straightforward: if it is not human waste or toilet paper, it should not go down the drain in a home with a septic system.

Signs your septic system has a floss or hair clog

If you have been flushing floss or other non-degradable items, watch for these warning signs that your system is developing a blockage:

  • Drains in your home are slow, especially showers and sinks.
  • Toilets gurgle or make unusual sounds when you flush.
  • Sewage backs up into your bathtub or lowest drain in your home.
  • Your septic tank alarm (if you have one) goes off.
  • Your drain field is wet or soggy even when it has not rained.

If you notice any of these signs, contact a septic service company when ready. The longer you wait, the more damage the clog can cause, and the more expensive the repair will be.

Frequently Asked Questions

Is biodegradable floss safe to flush down a septic system?

No. Even floss marketed as biodegradable or eco-friendly does not break down in the anaerobic environment of a septic tank. Biodegradable materials are designed to decompose in soil or compost with oxygen present. Throw all floss in the trash, regardless of what the package claims.

What if I have already been flushing floss for years without problems?

You may not have a pump tank, or the floss may not have accumulated enough to cause a visible blockage yet. Damage often builds slowly. Have your septic tank pumped and inspected by a professional to see if floss or hair has accumulated. Catching a problem early is much cheaper than waiting for a backup.

Can a plumber remove floss from my septic tank without replacing the pump?

Sometimes. If the floss is caught in the outlet pipe or tank, a plumber can pump out the tank and remove the blockage. If the floss has wrapped around the pump impeller, the pump may need to be disassembled or replaced. The cost depends on how severe the clog is and where it is located.

Do I need to tell my plumber I have been flushing floss?

Yes. Tell your plumber what items you have been flushing so they know what to look for and can give you an accurate estimate for the repair. This information also helps them advise you on preventing future clogs.

What should I use instead of floss if I have a septic system?

Water flossers (electric devices that spray water between teeth) are safe because the water goes down the drain and the device itself does not. Wooden floss picks can be composted. Traditional string floss should always go in the trash, wrapped so it does not unravel in your garbage bin.