What not to flush or pour down the drain with a septic system

EPA’s rule fits on a sticky note: don’t flush anything besides human waste and toilet paper¹. Everything else on this page is that rule applied to the things people actually wonder about.

It matters more on septic than on a city sewer because nothing leaves. Whatever goes down a drain ends up in a tank in your yard, and the tank relies on living organisms to treat it⁴. Penn State Extension sorts the troublemakers into three groups, and the grouping makes the list easier to remember⁵:

• things that clog pipes because they don’t break down,
• things that fill the tank early, so it needs pumping sooner,
• things that harm the bacteria that do the treating.

Never flush these

Item	Why
Wipes of any kind, including “flushable” ones	Can clog the system and cause a failure
Feminine hygiene products, condoms	Don’t easily break down
Diapers, bandages, cotton swabs	Don’t easily break down
Dental floss	Doesn’t easily break down
Paper towels and facial tissues	Don’t easily break down
Cat litter	Doesn’t easily break down
Cigarette butts	Don’t easily break down
Medicines	Can harm the bacteria in the tank

Sources: EPA, New York State Department of Health, Washington State Department of Health, Penn State Extension, NC State Extension.

The list is EPA’s¹, with cotton swabs and facial tissues from New York’s health department, which describes these as materials that don’t easily degrade³, and bandages from Penn State, which counts pills and liquid medicine among the things that can harm the tank’s bacteria⁵. On wipes, EPA says baby wipes and other wet wipes can clog the system and cause a failure², and Washington State’s health department puts “flushable” wipes on its never-flush list by name⁴.

At the kitchen sink

• Grease, fat and cooking oil. Never pour them down the drain¹. Let them cool and put them in the trash.
• Food scraps, eggshells and bones. Penn State lists them as waste that fills the tank prematurely⁵.
• Coffee grounds. They don’t decompose in the tank and take up storage space⁷.
• The garbage disposal. EPA says to eliminate or limit its use¹. New York’s health department explains why: disposals substantially increase the solids that build up in the tank and in the drain field³. Kansas State University Extension puts a number on it: with a disposal, cut the time between pump-outs by about a third⁷.

In the garage and under the sink

These don’t break down in a septic system and can reach groundwater⁷. EPA warns that even small amounts of some of them can².

• Oil-based paint, solvents and paint thinner. EPA adds that even latex paint waste should be kept to a minimum¹.
• Gasoline, motor oil and antifreeze¹.
• Pesticides and poisons⁶.
• Photographic chemicals¹.
• Chemical drain openers. For a clogged drain, EPA suggests boiling water or a drain snake¹.

Your county or town waste authority can tell you where household hazardous waste is collected.

Bleach and cleaners: where the agencies differ

This is the question people ask most, and the official answers don’t quite match.

• New York’s health department says household bleach, disinfectants, cleansers and antibacterial soaps, used in normal household applications, should not affect the system³.
• EPA draws the line at quantity: never pour “large volumes of toxic cleaners” down the drain¹.
• Washington State puts chemical cleaners on its “avoid” list, a step short of “never”⁴.
• Penn State lists bleach among the chemicals that can harm the tank’s bacteria⁵, and NC State lists disinfectants among the things to keep out⁶.

Read together, they point the same way. Cleaning a bathroom or running a load of whites is normal use. Emptying a bottle down the drain to get rid of it is not.

Medicines

Every agency on this page says not to flush them¹³⁴⁶. The FDA says take-back programs are the best way to dispose of most unused or expired medicines: year-round drop-off sites at some pharmacies, hospitals and police stations, prepaid mail-back envelopes, and the DEA’s National Prescription Drug Take-Back Days⁸.

Additives

Septic additives are sold as a way to help the tank. EPA doesn’t recommend them for household wastewater, because the tank already has plenty of microorganisms, and says they can be ineffective or even harm the system and the environment². It specifically warns against additives made of organic solvents or strong alkali chemicals². New York’s advice is the same: a properly sized and maintained tank does the job without them³.

Kansas State explains the catch. If an additive really did break down more of the solids in the tank, they would move on to the drain field, where they may speed up its failure⁷.

Too much water counts too

Washington State’s “avoid” list includes something that isn’t a product at all: excess water⁴. Water that rushes through the tank doesn’t give solids time to settle.

• A leaking or running toilet can add as much as 200 gallons a day¹.
• Doing all the laundry in one day can flood the drain field. Spread it over the week¹.
• Keep roof drains and sump pumps away from the drain field¹.
• Kansas State prefers liquid laundry detergent to powder, because powders contain bulking agents that don’t readily break down⁷.

Water softeners and other treatment equipment send rinse water to the septic system too. New York suggests a separate absorption area for that discharge where possible, but says it can go to the septic tank in many cases if the system is well maintained and can take the extra flow³. Our guide to hard water and water softeners goes through what the other agencies say.

What to do with it instead

Item	Instead
Wipes, floss, hygiene products, diapers	Trash. Keep a small bin next to the toilet
Grease and cooking oil	Cool, then trash
Food scraps and coffee grounds	Compost or trash
Medicines	Take-back site or mail-back envelope
Paint, solvents, pesticides, motor oil	Household hazardous waste collection
A clogged drain	Boiling water or a drain snake

Our summary of the sources above.

If the damage is already done

Slow drains, gurgling pipes, sewage odors or wet ground over the drain field mean it’s time to call a professional. See the signs of septic system failure and what to do first. If it has simply been a long time since the tank was emptied, our guide to how often to pump a septic tank will tell you whether you’re overdue.