Composting Toilet Diarrhea: What to Do With a Nature's Head

Composting toilet diarrhea is a moisture problem, not a disaster. Add dry coco coir or peat moss, turn the crank, keep the fan running, and empty early if the bin stays wet.

The Short Answer

Diarrhea, and even the odd bout of vomiting, is usually not a concern in a composting toilet as long as it does not go on for long. The solids bin is built for a balanced mix of waste and dry medium. Diarrhea tips that balance toward wet, so your job is to tip it back with more coco coir or peat moss.

Prolonged diarrhea is harder, because the toilet is designed for solid waste, not liquid. If the bin stays wet after you add medium, empty it early and start fresh. The same approach works for any urine-diverting composting toilet that uses a bulking material. On bag-based models like Separett, simply swap the bag sooner.

What Diarrhea Does to the Solids Bin

A composting toilet works best when the solids bin is moist but not wet, and full of air pockets. Too much liquid collapses those pockets and pushes the bin toward anaerobic conditions, which is when smells start. Here is how to tell the difference:

What to Do Right Away

Small, frequent corrections during the bout work better than one big fix at the end.

1. Open the trap door before you sit and stay seated. This keeps everything going into the solids bin rather than the urine diverter.
2. Add dry medium after each loose movement. Use a handful or two of dry coco coir or peat moss, not pre-soaked medium.
3. Turn the crank. Mixing coats the waste, spreads the liquid through the medium and brings air back in.
4. Check and repeat. Keep adding a little at a time until the mix looks like damp soil again.
5. Confirm the fan is on. It runs 24/7 and draws only about 1.68 amp-hours a day, so there is no reason to switch it off.

Worked number: coco coir absorbs up to 10 times its weight in water. One pound of dry coir can therefore hold up to about 10 pounds of liquid, which is why a few handfuls usually rescue a wet bin. Peat moss is ready to use straight from the bag, so it makes a good emergency backup.

When Liquid Goes Into the Urine Side

Loose stool can land on the front of the bowl and run into the urine diverter. When that happens, handle the bottle differently for a while:

• Empty the urine bottle sooner. Do not wait for the usual 2 to 3 day schedule. An overfull bottle can also leak into the solids bin.
• Pour it into a flush toilet or an RV dump station. Skip the diluted-fertilizer use this time, since that tip applies to urine from a healthy person.
• Rinse the bottle with diluted vinegar, not plain water.
• Clean the diverter channels with a 1:1 vinegar and water spray, and spray the interior sides of the bowl too.

Recovering the Bin: Keep Going or Empty Early

Once the bout passes, the bin usually recovers on its own. The material keeps composting as long as it stays aerobic, so keep cranking and keep the fan running.

A full-size Nature's Head solids bin handles about 60 to 80 uses, or roughly a month for two people full time. A stomach bug uses that capacity faster. The smaller Weekender chamber fills faster still. Empty early if any of these apply:

• The mix stays sticky or pasty after several rounds of dry medium and cranking.
• The crank handle gets hard to turn. Do not force it, because that can damage the agitator.
• Odor or fruit flies persist even with the fan running.

Early emptying follows the normal routine in our Nature's Head emptying guide and takes about 10 minutes. A wet load is where the bag liner method pays off. Line the bin with a 13-gallon compostable bag at setup, then lift the whole bag out, tie it closed and dispose of it. Clean the bin with vinegar and water, then restart with fresh medium.

Quick Reference and Prevention

To make the next stomach bug a non-event:

• Keep dry medium on hand. A spare coir brick or bag of peat moss stored dry is the single most useful backup.
• Use coco coir as your everyday medium. It holds its structure longer than peat moss and resists fruit flies better.
• Look after the fan. Clean it every other emptying cycle and clean the filters on each side of the base.

If symptoms persist, see a doctor. To compare models, browse the Nature's Head collection or read how urine-diverting and batch composting toilets differ.

Frequently Asked Questions

What happens if you have diarrhea in a composting toilet?

The solids bin takes on extra moisture, which can make the mix sticky and slightly smellier. A short bout is not a problem as long as you add dry coco coir or peat moss and turn the crank after each use. If the bin stays wet after several rounds of dry medium, empty it early and restart.

How much coco coir should I add after diarrhea?

Add a handful or two of dry coco coir after each loose movement, then crank and check. Repeat until the mix looks like damp garden soil with no visible waste. Coco coir absorbs up to 10 times its weight in water, so small additions go a long way.

Should I empty my composting toilet after a stomach bug?

Only if the bin does not recover. Empty early if the mix stays pasty after adding dry medium, the crank gets hard to turn, or odor and fruit flies persist. A bag liner makes a wet empty much cleaner, and the whole job takes about 10 minutes.

What if diarrhea gets into the urine bottle of a composting toilet?

Empty the urine bottle sooner than usual and pour it into a flush toilet or RV dump station, not on plants. Rinse the bottle with diluted vinegar and clean the diverter channels with a 1:1 vinegar and water spray. Avoid bleach, which kills the microorganisms the toilet relies on.

Can you throw up in a composting toilet?

Yes, an occasional bout of vomiting is usually not a concern in a Nature's Head composting toilet. Open the trap door so it goes into the solids bin, add dry coco coir or peat moss, and turn the crank. Treat it like any other extra moisture and empty early if the bin stays wet.

Why does my composting toilet smell after diarrhea?

Extra liquid collapses the air pockets in the solids bin and pushes it toward anaerobic conditions, which cause odor. Add dry medium, crank, and make sure the 12V fan and vent hose are working. If the smell persists after that, empty the bin early and restart with fresh medium.