According to the U.S. Environmental Protection Agency, more than 21 million households in the United States rely on septic systems. That’s roughly one in five homes operating their own miniature wastewater treatment facility—whether the occupants realize it or not.
And yes, that includes plenty of homeowners who didn’t even know they had a septic system when they bought the house.
Across Kitsap, Mason, and Pierce Counties, there are an estimated 166,000 septic systems quietly doing their job underground. Statistically speaking, there’s a decent chance yours is one of them.
At its core, a septic system is simple. Wastewater leaves your home and enters the septic tank, where solids settle as sludge, fats, oils, and greases float as scum, and the liquid in between—effluent—moves on to the drainfield. There, soil microorganisms finish the treatment process before the water slowly returns to the natural groundwater system. Simple doesn’t mean forgiving.
This entire process depends on naturally occurring bacteria to break down organic material. Anything that kills those bacteria, clogs the system, or refuses to break down doesn’t just disappear; it becomes your problem. And septic problems have a habit of becoming expensive problems.
So let’s talk about the items that should never enter your septic system, why they cause damage, and how a few everyday habits can mean the difference between quiet, uneventful plumbing… and a phone call you’ll remember for all the wrong reasons.
1. “Flushable” Wipes
Let’s start with the biggest offender wearing the most convincing disguise.
- Baby Wipes
- Cleaning Wipes
- Disinfecting Wipes
- Moist Towelettes
- Septic-Safe Wipes
Despite what the packaging says, flushable wipes do not break down like toilet paper. Multiple wastewater studies have shown that wipes can remain intact for months or even years in septic tanks. Toilet paper disintegrates in minutes. Wipes do not.
The Minnesota Pollution Control Agency created a demonstration video showing the difference in breakdown between regular toilet paper and similar-sized wipes.
Wipes are among the leading causes of septic back-ups into the home due to inlet baffles clogging, pump floats getting tangled, effluent filters becoming blocked, and solid carryover into drainfields.
To put a nail in the theoretical coffin, a Ryerson University study tested 101 products labeled as flushable and found that not a single one met industry standards for what should actually be flushed. Not one.
2. Personal Care Products
There’s a wide range of personal care products that should be avoided, including:
- Condoms
- Dental Floss
- Diapers
- Gauze
- Maxi Pads
- Tampons
These products are engineered to be durable, absorb liquid, and hold their shape. Once inside the system, they will expand, sink unpredictably, catch on internal components, and create blockages, quickly resulting in system failure. Since they’re not biodegradable, they’ll need to be manually removed.
3. Paper and Cotton Products
These paper products are sometimes used as alternatives to toilet paper, but should never be flushed into a septic system:
- Cotton Swabs & Balls
- Facial Tissues
- Paper Towels
- Napkins
- Rags
These items are made of fibers that don’t break down quickly enough, which can fill your tank’s sludge layer prematurely, requiring more frequent septic tank pumping. Many of these common products contain binding agents that help them hold together when they become wet.
Remember, toilet paper has one job. These paper products were not hired for it.
4. Fats, Oils, and Greases
Grease is a double agent. Hot, it flows. Cold, it solidifies. In a septic system, it floats, coats pipes, and interferes with bacterial digestion. Many of the typical culprits include:
- Bacon Grease
- Butter
- Cooking Oils
- Gravy
- Margerine
- Shortenings
- Salad Dressings
Once grease reaches the drainfield, it can clog the perforated leech field pipes and soil pores, and permanently reduce the drainfield’s absorption capacity. That’s not a clog that you can snake your way out of.
5. Medications and Pharmaceuticals
Flushing medications doesn’t just affect your septic system; it affects groundwater and nearby ecosystems.
- Medicines (Antibiotics, Hormones, Antidepressants, Antifungals, etc.)
- Vitamins
Many local health departments and pharmacies offer safe medication take-back sites for safe disposal. Septic systems are not one of them. Antibiotics, hormones, and antidepressants can kill beneficial bacteria in your septic tank and enter the surrounding groundwater systems unchanged.
6. Household Chemicals and Hazardous Waste
- Antibacterial Soaps
- Antifreeze
- Bleach (Excessive)
- Drain Cleaners
- Gasoline
- Motor Oil
- Paint
- Paint Thinners
- Pesticide
- Weed Killers
- Solvents
Your septic system runs on bacteria. Don’t wage chemical warfare against them. Occasional use won’t instantly destroy your system, but frequent, heavy use can reduce treatment efficiency, cause solids buildup, and ultimately lead to system failure. For example, a single gallon of bleach can kill the entire bacterial colony in a standard 1,000-gallon tank.
If your drain cleaner claims it “kills everything,” believe it. Including your septic bacteria.
Expert Tip: The University of Arizona recommends using oxidized bleaches, borax, baking soda, and vinegar for minor clogs rather than caustic chemicals. It’s cheaper and won’t turn your septic tank into a liquid graveyard.
Paint thinners, pesticides, photographic chemicals, motor oil, gasoline, and other toxic substances have no business anywhere near your septic system. Beyond killing the bacterial colonies that keep systems functioning, these chemicals can leach into groundwater and contaminate drinking water sources.
Most communities across Washington State offer hazardous waste collection days or permanent drop-off locations for these materials. Yes, it requires a minor amount of effort to store them temporarily and transport them to the proper facility. But compared to the alternative, a dead septic system and potential groundwater contamination, it’s an extraordinarily reasonable ask.
7. Cigarette Butts
Some people still flush cigarette butts, which is baffling on multiple levels. Most are not biodegradable, and the filters are made of cellulose acetate, a type of plastic that takes many years to break down. They release toxic chemicals into your septic system, potentially harming the bacterial colonies. And they can accumulate in your tank, get caught in filters, or, worse, pass through to your drainfield where they cause clogs.
Just use an ashtray like a civilized person!
8. Coffee Grounds and Food Scraps
- Coffee Grounds
- Eggshells
- Leftover Food
- Nutshells
This one surprises people. Coffee grounds and food scraps seem organic and harmless, like they should compost naturally in a septic system. They don’t. They don’t break down effectively; they settle to the bottom of the tank as sludge, and over time, they can accumulate significantly, requiring more frequent pumping.
More immediately problematic, coffee grounds create a fine sediment that can pass through the tank and into the drainfield, clogging the soil pores where biological treatment occurs.
Composting them is a better option, or simply tossing them in the trash. Your garden might appreciate them mixed into the soil, but your septic system definitely doesn’t.
9. Cat Litter
Cat owners face a unique temptation here. Some cat litter brands are marketed as septic-safe and flushable, promising convenience and easy cleanup. Cat feces can contain Toxoplasm Gondii, a parasite that isn’t killed during septic treatment and can contaminate groundwater.
Beyond the parasite issue, clay-based litters (even those labeled flushable) don’t break down and can accumulate in your tank and pipes, forming concrete-like masses. Some “flushable” litters are plant-based and do break down, but they can still add a significant organic load to your system and may still carry pathogens.
The safest approach? Bag it and trash it. If your cat is judging you for this decision, remind them that you’re the one who might have to pay for septic repairs.
Respect the Septic Tank
Managing a septic system isn’t rocket science; it’s mostly just restraint. If it didn’t come out of your body and it isn’t basic toilet paper, it belongs in the trash can. Your septic system is a marvelous piece of engineering that allows you to live a modern life without a municipal sewer connection. All it asks in return is that you stop trying to feed it dental floss and “flushable” lies.
Keep the bacteria happy, keep the grease in the can, and keep your $20,000 in the bank.