Do composting toilets smell bad?

We were concerned that every composting toilet reviewer had somehow lost their sense of smell at the same time they started using the unit. How could a bucket full of poo NOT smell bad? Well, either we both lost our nose function too, or the composting toilet we installed really doesn’t produce any nasty fumes.

How can a composting toilet not smell?

Mrs. Dieselfumes inherited her father’s ability to clear a room with his gaseous emissions. You’d think that would cause massive problems using a composting toilet in an area as small as a van, but it really hasn’t. Poop time and its immediate aftermath can be a little stinky, but interestingly not as bad as in our regular house toilet. Within a couple of minutes – or faster if we use the vent fan or open the doors – there’s no trace of the smell left.

The toilet itself doesn’t produce much smell in the first place. If you put your nose next to the opening and sniff, you smell a kind of loamy wet earth smell, not poop. The small fan in the toilet unit does a great job of keeping any smells out of the van.

We were concerned that the toilet vent pipe under the sliding door step might smell. That’s usually not the case. Most of the time we can sit in the van with the sliding door open or outside under the awning with no sewer smells at all. The only time it was an issue was after heavy use when we didn’t keep the coconut coir moist enough.

Tee fitting in place on the bulkhead fitting through the sliding door step wall
Composting toilet vent pipe behind the sliding door step wall – surprisingly little smell.

So far we’ve only had a single issue with the ceiling vent fan pulling fumes back into the vehicle. We know it’s been an issue for other composting toilet users. For us, again, it happened when we didn’t keep the coconut coir moist enough. We put the fan on to suck air out of the van but there was no way for fresh air to enter other than through the toilet vent. That pulled air over the toilet contents and left the van interior a little whiffy.

Our current design re-think for the van means we’ll have a permanent vent in the floor of the van to draw fresh air in to the vehicle. So long as that floor vent is open, it’s unlikely the ceiling fan would create enough negative pressure to make the toilet back-vent.

What about noise?

The vent fan runs constantly. When the toilet cabinet is open we can just about hear it whirring. With the cabinet closed, we have to really strain to hear it. It’s much quieter than our fridge.

Pee and poo quantities – how often does it need emptying?

We’ve learned to pee outside the van whenever we can so that the toilet’s pee container doesn’t get full so quickly. Overnight though it’s less disturbing for the other person if we pee inside the van rather than to go outside with all the door slamming that entails. It’s still best to change the pee container every few days so that it doesn’t get super-stinky.

We have emptied the poo container once so far, after several weeks of full time use interspersed with little to no use. We probably wouldn’t have had to empty it if we’d kept the coconut coir moist and stirred it regularly.

We both have high fiber diets and frequent poops, but we’re starting to believe the claims that the unit can last for a couple of months of regular use.

Cleaning the toilet

Nature’s Head provide a small (12oz?) squirt bottle with the toilet. For a while we used a mix of water with 2 Tbsp. of white vinegar in it to spray around the bowl. After a while though the vinegar goes “off” and smells pretty strong. We’ve moved to using 3% hydrogen peroxide instead.

One issue – the provided spray bottle can leak through its nozzle. Going from sea level to 5000ft and back down again resulted in a tiny puddle under the bottle. Easy to fix by tightening the nozzle down or storing the bottle somewhere waterproof. When we moved to using hydrogen peroxide, we started using a different sprayer that doesn’t let light through (hydrogen peroxide degrades in the light).

The toilet bowl is made of shiny plastic. The trap door area is pretty large. Small “misses” where poop hits the toilet pan at the side of the trap door are infrequent but they are easy to clean up with a piece of toilet paper followed by a spray of hydrogen peroxide mix.

Keeping the bowl clean is easy with hydrogen peroxide spray and the occasional Clorox wipe.
Keeping the bowl clean is easy with hydrogen peroxide spray and the occasional Clorox wipe.

Talking of misses, Mrs. Dieselfumes would argue that it’s harder for women to keep pee out of the poop container for anatomical reasons. Obviously the idea is to pee first, then shift back a little to poo, but that isn’t always possible. She still seems to have managed really well.

Mrs. Dieselfumes reports that periods are no messier than in a regular toilet.  Our house is on a septic system, so she doesn’t flush sanitary items at home anyway. In the van she wraps them in paper towel and stores them in a ziploc bag before trashing them.

We do carry Clorox wipes in the van, and every now and again we’ll wipe the seat and bowl around with one. For us this is the equivalent of cleaning the toilet at home with bleach, and it happens with about the same frequency.

We’ve read about people waxing the bowls on their portable toilets to make them even more non-stick. We’re not sure that would help much and clean-up hasn’t been an issue for us yet anyway.

What we’ve learned

Even though the toilet hasn’t been installed that long, we’ve had plenty of opportunity to experiment with it. Here are some tips, based on what worked and didn’t work for us.

  • Keep the coconut coir or peat moss moist. If it dries out, it starts to go solid and it’s difficult or even impossible to re-hydrate it sufficiently. Although it seems counterintuitive, keeping it moist also seems to keep the smell levels down.
  • Minimize the quantity of paper you put in the toilet. It doesn’t degrade, and it gets wrapped around the stirring blades. If the paper only has pee on it, consider throwing it in the regular trash or keeping it in a ziploc bag instead of dropping it into the composting toilet. We use a trash container with a sealed lid, so there are no odor concerns with doing this.
  • Keep the toilet bowl clean. One of the biggest sources of smell is stale pee in the bowl area. A small spray bottle of 3% hydrogen peroxide seems to do the trick really well. Every now and again, you might want to use a Clorox wipe for a deeper clean.
  • Use a dash of chlorine bleach in the pee container. Dilute it with a touch of water. Our pee doesn’t seem to stink too much anyway, but the couple of drops of bleach really stops any smell at all.
  • If you aren’t using the van for a while, remember to stir the toilet occasionally and check the moisture level of the coconut coir. Believe me, you don’t want to have to chip pieces of dried up brown stuff off the stirrer blades because you left it too long and it solidified.

If some of those tips make you think “Oh, a composting toilet sounds like hard work” then think about the maintenance requirements for a tank or cassette toilet. You still have to do all the cleaning of the bowl, disposing of waste is heavier and stinkier, and there’s still the potential for either the smell of blue chemicals or the toilet contents to permeate the vehicle.

So far we’re really happy with the composting toilet. We’ll update this post if we change our minds at all.

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