Sun-Mar Spacesaver or Mobile composting toilet in an RV or trailer

Hi everyone,

I'm wondering if anyone has experience with a Sun-Mar Spacesaver or Mobile in an RV bathroom. I'm considering replacing the flush RV toilet with a composting toilet and specifically interested in these models for the ability to only take finished compost out and small size to fit in a tiny bathroom. This is on some off-grid land around 9500' elevation in Colorado and the trailer will rarely be moving. We'll sometimes have guests who have no experience with a composting toilet and can't really ask them to empty a Nature's Head or similar system.

I've heard about the problems some have had with making sure visitors don't turn the crank and end up with the drum opening not facing the top. I'm especially interested to know how you chose either the Spacesaver or the Mobile, if you've had any trouble with smell in a relatively closed space like an RV or trailer, and any other perspective you can offer.

Thanks!

- Bruce

Welcome to permies!

Here are some threads you might find interesting:

https://permies.com/t/24168/Sun-Mar-similar-venting-heat

https://permies.com/t/49353/Black-soilder-flies-composting-toilet

https://permies.com/t/118164/Urine-diversion#957681

Thanks for the links! I actually came across those in my search before I posted, but definitely worth reviewing.

I'm hoping to find someone with experience specifically in a small RV/trailer bathroom, but so for, no luck.

Thanks again,

- Bruce

We have an old SunMar NE (non-electric) at our cabin. I love not having to go outside to the outhouse. I despise when we have to do a deep clean (i.e., we didn't empty often enough or our "mix" wasn't quite right and the liquid diverter drain clogged.) I can't find an install manual for the mobile so I'm not sure if it has the urine diverter. Ours can develop an odor, but it seems that is only when it isn't being emptied often enough or you have, like in our case, a clog. We have it in an enclosed, attached shed so it isn't a small space space and it is not built very tight so there is air leaks 24/7. We also have an additional large, louvered and screened vent next to it for heavy-use months since ours doesn't have the electric powered vent. It can be messy to clean out, they do not hold a ton so guests may have to take the finishing tray out to dump. They recommend adding peat moss in that needs to be stored and creates a bit of dust when dumped in. All that aside, I do overall recommend them but I'd wait to hear from someone that has used them in a boat or RV. For our off-grid cabin it is just about perfect, but in a tight spot it might not be ideal.

There are 55 posts here at permies that mention Sun Mar though none of them have used them in an RV or Boat.

Having been around RVers for many years, I think it would be rare to find an active RVer using one.  

If you really want to find someone using a Sun Mar then I would try Here:

https://www.rvnetwork.com/

I did a search for sun-mar and found no posts.

Do you know if they are sold at any of the popular RV stores like Good Sam's?

Here is an example of why you might not find anyone:

Composting Toilet In A RV - What They Don't Tell You (Full Time RV Living]

Denise, thanks for the perspective on the SunMar NE. We're actually planning something similar to what you describe in addition to the trailer bathroom. One thing I've read a little about any of the the Sun Mar toilets is people having trouble with visitors turning the drum and using the toilet without the drum opening pointing up, making a mess that's a pain to clean up. Have you experienced anything like that? I'm also curious to hear more about the clogging problem, which is another thing I've come across.

Anne, thanks for the perspective on this. I don't think they're sold at RV stores and most instances I've found of people using composting toilets in RVs have been the Nature's Head, like in the video you linked to, and that's definitely something we're considering. The downside is that we'd then either have to take our waste to the dump a 40 minute drive away or set up a separate composting system on our land for just that waste. We were using a bucket toilet last year and had a bit of a disaster with waste in the car on the way to the dump, so we'd probably lean towards on-site composting.

I'll look into the RV network and see what I can find.

Haven't ever had a problem with people using it wrong, but we've only had family there. We have a helpful "reminder" note there to add a cup of peat after poo and turn the drum a full rotation. You could do the same but include the part to look down and make sure you can see into the drum or turn until you do. The clog...well, lets just say I was super thankful we had the huge vent next to it we could open up. In our unit there are 2 drains at the back of the evaporative tray that take excess liquid to a lined pit (which might be a bother if you need to move the trailer). In the course of normal operation you add peat to help the composting and keep the smell down, if you forget to scrape out the lower chamber every so often the stuff that missed the finishing drawer and collected in the corners can clog the drain lines. The liquid backs up and you have a very smelly, messy, issue to deal with. Nature's head has a note that you can improvise a drain tube from the urine collection bottle and then you could plumb it like the Sunmar does to a pit or other options so it would only need the solids emptied about as often as the Sunmar. Here's the manual showing the urine diversion/collection options. But you may need to check your local codes.

Just wanted to follow up on this thread from a while ago and say that we ended up going with the Separett Tiny in our trailer and the Separett Villa in our outhouse. We wanted to keep the same kind of toilet in both locations and the Spacesaver and Mobile just seemed a little too tight for our trailer bathroom. Additionally, the Separett has fewer moving parts and seems like less of a potential problem if something went wrong.

This did, however, mean digging two french drains (we went with the urine tube in the trailer instead of the tank version) and doing a bit of plumbing work to send the urine out.

So far, we've liked the Separett toilets and the few guests we've had have been happy with them as well. Possibly the best thing about the tiny in the trailer is that there is no smell at all! Like, less smell than using a "normal" water toilet at home, despite being in a tiny room in the trailer that barely has enough room for a medium-sized person to sit down.