What Can You Put Down a Septic Tank?
Last updated: January 2026
If you have a septic system, you've probably heard plenty about what NOT to flush.
But what about what you CAN put down your drains?
The answer is simpler than most people think, and more restrictive than many homeowners realize.
Here’s the straightforward truth about what belongs in your septic tank, what doesn’t, and why it matters.
The Quick Answer
What can you safely put down a septic tank?
Three things only:
- Human waste (urine and feces)
- Toilet paper (standard, not ultra-thick or “luxury” brands)
- Water (from toilets, sinks, showers, laundry)
That’s it.
Everything else is either:
- Harmful to your system
- Risky enough to avoid
- Unnecessary and potentially problematic
The simple rule: If it didn’t come out of your body or isn’t plain toilet paper, don’t flush it.
Why This Matters
How Septic Systems Work
Your septic system relies on biological digestion:
- Waste enters the tank
- Bacteria break down organic matter (human waste, toilet paper)
- Solids settle as sludge
- Liquid effluent flows to the drainfield
- Soil provides final filtration
This biological process has limits.
Bacteria can digest:
- Human waste ✅
- Plain toilet paper ✅
- Some biodegradable material (slowly) ✅
Bacteria cannot digest (reliably):
- Plastics and synthetic fibers ❌
- Grease, oils, and fats ❌
- Harsh chemicals ❌
- Most “flushable” products ❌
What Happens When You Flush the Wrong Things
Short-term problems:
- Clogs in pipes or the tank
- Backup into the house
- Strain on the bacterial ecosystem
Long-term damage:
- Drainfield failure (biomat clogging and soil saturation)
- Premature system failure
- $10,000–$25,000 drainfield replacement
The cost of flushing the wrong thing once: maybe nothing.
The cost of doing it regularly for years: system failure.
What’s Always Safe
Human Waste
Urine and feces are what septic systems are designed to handle.
- Break down through bacterial digestion
- Provide nutrients for the system biology
- No risk in normal quantities
No restrictions here—this is what the system is for.
Standard Toilet Paper
Plain, standard toilet paper is safe because it’s designed to break down in water and is compatible with septic biology.
Best practices:
- Use standard 1-ply or 2-ply
- Avoid ultra-thick, quilted, or “luxury” toilet paper (breaks down slower)
- Don’t use excessive amounts
Learn more: Can You Flush Toilet Paper Down a Septic Tank Safely?
Water
Water from normal household use is safe:
- Toilet flushing
- Showers and baths
- Sinks (bathroom and kitchen)
- Laundry
- Dishwasher
Important: Even “safe” water can become a problem if you overload the system.
- Fix leaky toilets and faucets
- Spread out laundry (avoid many loads in one day)
- Avoid excessive bleach or harsh chemical dumping
What’s Risky (Use Caution or Avoid)
Food Waste
General rule: Don’t put food down any drain.
Why: It adds solids to the tank, increases pumping frequency, and often introduces fats that don’t break down well.
Never put down drains:
- Grease, oil, fat
- Coffee grounds
- Eggshells
- Meat scraps and bones
- Pasta and rice (can swell and contribute to clogs)
Best practice: Scrape into trash or compost before washing dishes.
Garbage Disposal
Can you use a garbage disposal with a septic system? Technically yes, but it’s not recommended.
Why it’s a problem:
- Increases solids significantly (tank fills faster)
- Can push more organic load into the drainfield
- Often forces more frequent pumping (sometimes every 1–2 years)
Household Cleaning Products
Most normal household products are okay in moderation, but some are risky.
Generally okay (normal household use):
- Dish soap
- Laundry detergent (standard)
- Shampoo and body wash
- Mild bathroom cleaners
Use cautiously:
- Bleach (small amounts; avoid frequent heavy use)
- Antibacterial products (can suppress helpful bacteria)
Avoid entirely:
- Chemical drain openers (e.g., caustic drain cleaners)
- Industrial-strength solvents/cleaners
Learn more: Can You Use Bleach with a Septic Tank Safely?
Medications
Don’t flush medications.
- Some pharmaceuticals can interfere with septic biology
- Many don’t break down well and can reach groundwater
Use pharmacy take-back programs or approved disposal methods instead.
What’s Never Safe
“Flushable” Wipes
Despite the label, wipes are not septic-safe. They don’t break down like toilet paper and can accumulate in pipes, the tank, and the drainfield.
Always throw wipes in the trash.
Learn more: 13 Things You Should NEVER Flush Into a Septic System
Feminine Hygiene Products
Never flush pads, tampons, applicators, or liners. They don’t break down and commonly cause clogs and pump-out complications.
Paper Products Other Than Toilet Paper
Don’t flush:
- Paper towels
- Facial tissues
- Napkins
- Cotton balls/swabs
- Dental floss
These are designed to stay strong when wet, exactly the opposite of what a septic system needs.
Fats, Oils, and Grease (FOG)
Never pour grease or oil down any drain—even with hot water. It cools, solidifies, and accumulates in pipes and the tank.
Proper disposal: Cool it, pour into a container, and throw it in the trash.
Chemicals and Hazardous Materials
Never flush paint, solvents, motor oil, pesticides, or automotive fluids. These can kill septic biology and contaminate groundwater.
Cat Litter
Never flush cat litter (even “flushable” brands). It can clog pipes and introduces pathogen risks.
Frequently Asked Questions
Can I use septic-safe additives or treatments?
Most additives are unnecessary for a healthy system. However, plant-based micronutrient support (like Biologic™ Septic) can help bacterial efficiency in stressed or aging systems without harsh chemistry.
Learn more: Do Septic Tank Additives Really Work?
What about biodegradable products?
“Biodegradable” does not automatically mean “safe for septic.” Many items only break down under industrial composting conditions. When in doubt, throw it out (in the trash).
Can I pour small amounts of cooking oil down the drain if I run hot water?
No. Hot water doesn’t prevent grease from cooling and solidifying later. Small amounts accumulate over time.
What if something accidentally gets flushed?
One accidental flush usually won’t cause immediate failure. Don’t panic—just don’t repeat it. If you notice slow drains or backups afterward, call a professional.
Are natural or eco-friendly products safer for septic systems?
Often, yes, especially if they avoid harsh solvents, heavy antibacterial agents, and frequent bleach use. But “natural” doesn’t guarantee septic-safe in high concentrations.
How do I know if I’ve damaged my system by flushing the wrong things?
Warning signs include slow drains, frequent backups, sewage odors, soggy drainfield areas, and needing to pump more often than expected.
Learn more: How Do I Know If My Septic System Is Failing?
The Bottom Line: Keep It Simple
Your septic system isn’t a trash can.
It’s a biological treatment system designed for three things:
- Human waste
- Toilet paper
- Water
Everything else is a risk—even if it seems harmless, claims to be “flushable,” or is labeled biodegradable.
Key Takeaways
- ✅ Only flush human waste, toilet paper, and water
- ✅ “Flushable” does not mean septic-safe—trash wipes
- ✅ No food waste, grease, or oils down any drain
- ✅ Use cleaning products moderately—avoid harsh chemicals
- ✅ When in doubt, throw it out (in the trash)
- ✅ Protect your system = protect your investment
Additional Resources
- SeptiCorp Homeowner Septic Guide
- 13 Things You Should NEVER Flush Into a Septic System
- Can You Flush Toilet Paper Down a Septic Tank Safely?
- How to Maintain a Septic System: The 5-Pillar Approach
- Biologic™ Septic Treatment
Have questions? Email us at support@septicorp.com or call (888) 380-0175.
Colin Box
Founder, SeptiCorp