What Not to Flush or Pour Down the Drain With a Septic System
Short answer: A simple rule of thumb: flush only human waste and toilet paper. Grease, chemicals, and anything that doesn't break down, like wipes, feminine hygiene products or cat litter, can clog or poison a septic system.
Never flush
Feminine hygiene products, condoms, dental floss, diapers, wipes, even ones labeled flushable, cigarette butts, coffee grounds, and cat litter. None of these break down the way toilet paper does, and they build up as solids in the tank or clog the pipes and drainfield.
Never pour down any drain
Grease, fats, butter, wax and heavy cream, which solidify and clog pipes. Household chemicals including pesticides, drain cleaners, paints, paint thinners, solvents and gasoline, which can kill the bacteria your septic tank depends on to break down waste, and can end up in your groundwater. Large volumes of medication should go to a take-back program, not down the drain or toilet.
Why it matters more with septic than sewer
A municipal sewer system routes everything to a treatment plant designed to handle a wide range of contaminants. A septic tank relies on a living population of bacteria to break waste down on your own property; chemicals that kill that bacteria stop the tank from working properly, and non-biodegradable items just accumulate as solids that need to be pumped out sooner.
Sources
Checked July 2026.