Empty the tank when it reaches three-quarters full, not when it overflows
A composting toilet fills more slowly than a standard flush toilet because the waste breaks down as it sits. Most residential units need emptying every three to twelve months, depending on household size and use. The tank itself will tell you when: look for the fill line marked on the side, or check the visual indicator if your model has one. Some toilets have a float valve that rises as the tank fills — when it reaches the top, emptying is overdue.
Do not wait until the toilet stops working or backs up. Once the tank is three-quarters full, the composting process slows, odour increases, and you risk overflow into the bowl. Emptying on schedule keeps the system working as designed and makes the job easier.
Key Takeaways
- Empty the tank when the fill line reaches three-quarters full, typically every three to twelve months depending on household size.
- Wear gloves, a dust mask, and eye protection — the contents are not sterile and dust can irritate lungs and eyes.
- The finished compost at the bottom of the tank is safe to handle once it has aged for at least six months after removal.
- Most jurisdictions allow you to compost human waste in your own garden but prohibit selling or distributing it.
- If your toilet has a separate urine diverter, empty that container monthly to prevent odour and reduce the weight of the main tank.
Gather the right tools and protective gear before you start
You will need a five-gallon bucket with a lid, a small shovel or scoop, heavy-duty gloves, a dust mask rated N95 or higher, and eye protection. Some people also wear a long-sleeved shirt and keep paper towels nearby. Have a garden hose and water source within reach — you may need to rinse tools or your hands afterward.
If your composting toilet sits indoors or in a basement, open windows and doors to ventilate the space before you begin. If it is in an outhouse or shed, work on a calm day so wind carries odour away from the house. Do not empty the tank in rain or when ready after heavy rain, because water in the tank makes the contents heavier and wetter.
Remove the tank and carry it to your compost location
Most residential composting toilets have a removable tank that slides out from underneath or lifts away from the bowl. Check your toilet's manual for the exact method — some have latches or clips you must release first. If the tank is too heavy to lift safely (more than 40 pounds), ask someone to help or use a hand truck.
Carry the tank slowly to your designated compost area, which should be away from the house, a well, or a neighbour's property line. Set it on level ground where you can work without spilling. If the tank has a drain plug at the bottom, place a bucket underneath before you open it — liquid will pour out.
Drain the liquid and scoop out the solid waste
If your tank has a drain plug, open it slowly and let the liquid drain into a bucket. This liquid, called leachate, can go down a drain, into a grey-water system, or onto your garden away from vegetables you eat raw. If there is no drain plug, you will scoop out the contents from the top.
Using your small shovel or scoop, remove the solid waste layer by layer into your five-gallon bucket. Work slowly to avoid stirring up dust. The material at the bottom will be darker and more decomposed than the material at the top — this is normal. Once the tank is empty, you can rinse it with a hose if needed, though many people skip this step to save water.
Store the removed waste for at least six months before using it
The contents you removed are not yet finished compost. They must age for a minimum of six months — longer is safer — before you use them in a garden. Place the material in a covered bin or pile in a corner of your yard, away from foot traffic and play areas. Cover it with a tarp or lid to keep rain out and prevent flies from laying eggs.
After six months, the material will look like dark, crumbly soil with little visible waste. At this point, it is safe to mix into garden beds, around ornamental plants, or under trees. Do not use it on vegetables you eat raw, such as lettuce or tomatoes, unless your local health department has given written permission. Most jurisdictions allow home use but prohibit selling or giving away human waste compost.
Empty the urine diverter if your toilet has one
If your composting toilet has a separate urine diverter — a funnel or tray that channels urine away from the solid waste — empty it monthly or when it is full. Urine is sterile and can go directly onto your garden, diluted with water at a ratio of one part urine to ten parts water. Undiluted urine can burn plants.
Some people use diverted urine as a nitrogen-rich fertilizer for ornamental plants or compost piles. Others prefer to flush it down a drain. Check your toilet's manual to see whether the diverter drains into a separate container or directly into a tank below. If it drains into the main tank, you do not need to empty it separately.
Reinstall the tank and resume normal use
Once the tank is empty and dry, slide or lift it back into place under the toilet bowl. Make sure it is seated properly and any latches or clips are fastened. If your toilet has a separate liquid tank or urine container, refill or reinstall those as well.
Before you use the toilet again, add fresh bulking material — usually coconut coir, peat moss, or sawdust — to the bottom of the tank. This material absorbs moisture, reduces odour, and speeds decomposition. Use about two to three inches, or follow the amount recommended in your toilet's manual. Your toilet is now ready for use.
Frequently Asked Questions
Is the waste in the tank safe to touch?
The waste contains bacteria and pathogens that can cause illness if you touch your face or eat without washing your hands afterward. Wear gloves and a mask, and wash thoroughly when you are done. Material that has aged for six months or longer is much safer to handle than fresh waste.
What if the tank is too heavy to lift?
Ask a second person to help, or use a hand truck or dolly to move it. If the tank is permanently installed and cannot be removed, check your toilet's manual — some models have a clean-out port or access panel that lets you scoop out waste without lifting the entire tank.
Can I pour the waste down a drain or into a septic system?
No. Composting toilet waste is not designed for septic systems or municipal sewers. It must be composted on-site or taken to a facility licensed to accept it. Check with your local health department to learn whether your area has a composting facility that accepts human waste.
How often do I really need to empty it?
It depends on how many people use the toilet and how often. A household of two might empty once a year; a household of four might empty every three to four months. Watch the fill line and empty when it reaches three-quarters full, rather than following a fixed schedule.
What if my composting toilet smells bad?
Odour usually means the tank is too full, the bulking material has broken down, or moisture is too high. Empty the tank, add fresh bulking material, and make sure the ventilation pipe is clear and unobstructed. If the smell persists, check that the toilet lid closes tightly and that no cracks allow air to escape.