What not to flush or pour on a septic system
Search an item to see whether it belongs in a septic system. The short answer is always the same: only human waste and toilet paper go in the toilet.
Designed to break down. Use a reasonable amount.
This is what the system is built for.
“Flushable” wipes don’t break down like toilet paper. They clog pipes and fill the tank.
Non-degradable. Bin them.
Made to hold together when wet, so they break down slowly and add solids.
Clog pipes and the tank inlet.
Don’t break down; clog pipes and fill the tank.
Non-degradable.
Non-degradable; tangles with other solids.
Don’t break down.
Non-degradable filters and chemicals.
Clay and silica litters don’t break down, and cat waste can carry parasites.
Add solids that settle as sludge.
Builds up the scum layer and can clog the drainfield. Let it cool and put it in the trash.
Garbage disposals add a large solids load and mean more frequent pumping. Compost or bin scraps where you can.
Can harm the bacteria in the tank and pass into groundwater. Use a drug take-back site.
Toxic to tank bacteria and to groundwater. Take to household hazardous waste.
Hazardous waste. Never down any drain.
Kill the bacteria that treat wastewater and contaminate groundwater.
Harsh chemicals can kill tank bacteria. Try boiling water or a drain snake first.
Normal household use is fine. Large amounts can upset the tank’s bacteria.
Fine in normal amounts. Spread loads through the week so you don’t flood the tank in one day.
Brine can affect some systems. Ask your installer or health department whether yours can take it.
A big volume all at once can flood the drainfield. Drain it elsewhere, following local rules.
EPA and Penn State say they aren’t needed, and some can harm the system. They don’t replace pumping.
Clumps and clogs. Use a drain catcher.
Non-degradable.
Why it matters on septic
On city sewer, the wastewater plant deals with whatever you flush, at least in theory. On septic, your tank is the treatment plant, and it sits in your yard. A septic tank works by letting solids settle and grease float while bacteria break down what they can. Anything that doesn’t break down just takes up space. The tank fills faster, needs pumping more often, and if solids escape to the drainfield they can clog the soil. Once the drainfield is clogged, pumping the tank won’t fix it. Repairs or replacement are often among the most expensive jobs a homeowner faces.
The three groups to watch
Penn State Extension sorts what goes into a septic tank into three groups. First, biodegradable organic solids such as human waste. Second, slowly biodegradable solids such as toilet paper and other cellulose. Third, solids that don’t break down at all, such as cat litter and plastics, which fill the tank quickly. Cutting back on the second and third groups greatly slows how fast your tank fills. EPA’s SepticSmart advice says the same thing more simply: the toilet is not a trash can.
Drains count too
Everything that goes down the kitchen sink, the tub, and the washing machine ends up in the same tank. EPA advises keeping grease, oil, and food waste out of sink drains. Chemical drain openers, paints, solvents, and pesticides shouldn’t go into any drain, because they kill the bacteria that treat the wastewater and can reach groundwater. Many households with septic also have a private well nearby. See protecting your well from your septic system.
Water volume matters as much as what’s in it
Big surges of water, such as several loads of laundry in one day, a drained hot tub, or a running toilet, push wastewater through the tank before solids have time to settle. EPA estimates that an average household uses about 70 gallons of water per person per day indoors, and that a single leaky toilet can waste as much as 200 gallons a day. Our saving water on septic guide has the details.
Print this list for the bathroom or kitchen if you have guests or tenants. If you’re unsure about an item, put it in the trash.