Combining black and gray, composting toilet with urine diverting

[JoleneAS]

Hey guys. Gutting a 76 Overlander. My plan is to do a composting toilet with urine diverting to the black tank. I have read about people combining their gray and black tanks when using a composting toilet, though I haven’t seen any posts where the two tanks were combined while still urinating into them. Is this something that would be problematic? I’d love to have the extra gray water storage. Thanks!

[Shiny16]

It shouldn’t be a problem. The sport 16 has only one tank. Just to be clear it would no longer be considered grey.

[xrvr]

Search function.

[JoleneAS]

Originally Posted by Shiny16

It shouldn’t be a problem. The sport 16 has only one tank. Just to be clear it would no longer be considered grey.

True that. I will keep that in mind. Thanks!

[JCWDCW]

Just curious since this came up in a conversation a few days ago....how will you interconnect the tanks and still get a good flush of the upstream tank..or will
you open two valves to drop the tanks?
JCW

[JoleneAS]

Originally Posted by JCWDCW

Just curious since this came up in a conversation a few days ago....how will you interconnect the tanks and still get a good flush of the upstream tank..or will
you open two valves to drop the tanks?
JCW

I've kind of wondered as well. I had considered a valve between the gray and black that can be opened / closed. You could drain the black first, then flush the gray through the black afterwards? I dunno. I'm new to this RV holding tank stuff. :B

[Banker]

Fluid is necessary in order to complete composting. The urine of course provides the necessary fluid.

[JoleneAS]

Originally Posted by Banker

Fluid is necessary in order to complete composting. The urine of course provides the necessary fluid.

I'm not sure how that works. The Nature's Head toilets divert the urine away from the composting area by default, and plenty of folks send their urine straight to the black tank. There's also venting to dehydrate the compost, so I don't think urine is a necessary ingredient for the composting process. Is there something I'm missing here?

[guskmg]

Natures Head compost toilets are not sealed like AirHeads. AirHead seals all matting surfaces including the seat and lid. I have had one for a year now and there is never any smell. When you open up a toilet for any reason you should have the ceiling fan sucking air into the bathroom. The toilet vent fan should be powered 24/7, directly from the battery. Solar powered fans won't work all the time. If the toilet is venting and composting correctly, you will not even smell anything coming out the external fan vent. My experience has only been with Coconut Coir and Zep Drain Care enzyme.
On the plumbing of urine directly into the black tank and mixing the grey and yellow together remember urine is sterile unless diseased. Therefore, disposal could be any where that is not objectionable. Remember, we eat fish and drink water from lakes and rivers that have urine from its inhabitants. That is why boat owners like compost toilets. Very convenient.
guskmg

[TheGreatleys]

Originally Posted by JoleneAS

I'm not sure how that works. The Nature's Head toilets divert the urine away from the composting area by default, and plenty of folks send their urine straight to the black tank. There's also venting to dehydrate the compost, so I don't think urine is a necessary ingredient for the composting process. Is there something I'm missing here?

Composting (a la The Humanure Handbook) does NOT occur in a composting toilet to any significant amount. Poop stays poop until you bag it and throw it away, or bury it, or fling it at oncoming traffic, whatever your disposal preference.

If you want to actually compost, then yes, it's helpful to mix solids and liquids. If you want to do that in the toilet, it requires a LOT of cover material to keep it from smelling. Then you empty the whole shebang in a properly constructed compost pile and let it do its thing for a year. If you play your cards right, you end up with nicely decomposed compost that you can use on your garden, though preferably not directly on root vegetables just to be safe.

Most of us using NH/AH toilets just want a functional toilet and don't have compost piles to complete the cycle. In that case, it's advantageous to keep solids and liquids separate to minimize maintenance and keep bad smells from developing. Liquids go in a toilet or in the woods, solids get landfilled like dirty diapers and bags of dog doo. It's not as good of a solution from a sustainability perspective as actual composting, but it's arguably better than chemically embalming your sewage, and it works great for a lot of folks.

[dbj216]

Valterra (and maybe Thetford) make a blade valve with a bayonet fitting on both sides that twists on your sewer discharge port, and then the sewer hose (slinky) twists on to that. Or you can make one yourself. If you shut this "third" blade valve and open both the black and grey tank valves, the two tanks become one common holding tank.

Maybe that is how folks add waste water holding capacity when using a "composting" toilet.

The Greatleys Nature's Head toilet use experience is very good. We all have no excuses for not knowing what this thing is all about. Me and my grandson toss a bag full of dirty diapers in the garbage every week. My baby sons used cloth diapers and the contents were scrapped into the toilet. Me and my beagle toss doggy bags in to the garbage at the campground after every walk. I like Greatleys idea of poo disposal. Fling it into oncoming traffic. Marvelous idea.

I will say that our local "publicly owned treatment works", or sewer plant, does a great service in treating waste to keep us healthy. That is one advantage of a flush toilet and a sewer hookup.

David

[JoleneAS]

Thank you all for the feedback. Much appreciated, and also nice learning a bit more about composting. If you guys were me and wanted to divert urine, would you go ahead and combine the gray + black, or would you do what I’ve seen someone else recommend on a different thread, which would be keeping the black and gray separate and having kitchen water go to gray while all bathroom water (sink, shower, urine) go to black?

[HappyHapgood]

I probably over complicated the issue...
Last week I installed a solution that I hope will allow my wife and me to extend our boondocking. I plumbed a “spare” water pump to move liquid from my grey tank to my black tank. I did this because my experience is that we end up with a 90% full grey while the black tank is at 15%.
The pump is under the closet where the regular water pump is located. There are check valves and a filter to a) ensure fluid only can move from grey to black and not vice-versa, and b) try to keep any solids from mucking up the pump. I used

1) a momentary switch to minimize the likelihood of overflowing the black tank.
2) clear tubing to watch the process
3) an easily accessible and cleanable filter

I’ve tested it only briefly and it seems to work as intended. Next week we will go boondocking so I’ll know then if it works when I really need it and without unintended consequences.

[dbj216]

Hi JoleneAS: I think the fastest way to fill a grey tank is taking a shower. Let's see, our water system likely delivers a good 2 gallons a minute out the shower head. A quick 5 minute shower is 10 gallons of water in the tank. The second fastest is doing dinner dishes. Our 70s Airstreams don't have "modern" size grey water tanks in most cases. My Overlander had 10 gallons, my friends 76 Sovereign is more like 20 gallons. Maybe you know the size of the tanks under your Overlander.

I often shower in the campground bath. A guy can do a lot of body cleaning in the trailer with a washcloth and a bar of soap, but no shower. If I shower in the trailer, it is a "military" shower. A long, hot shower is a luxury and many times not needed. The answer to your question depends on how you and your family intend to use the trailer.

It is perfectly logical to utilize your black tank capacity with bath sink, shower and a bit of urine. It may take some significant replumbing to do so. I plumbed the vanity sink into my black tank just to utilize some capacity. It is too late for me to put the shower water there.

It may be easier yet just to add a third blade valve and utilize both tanks together. I will do this if I get the grey tank filling too fast.

David

[guskmg]

You can use a third valve as mentioned or use an end cap with a hose fitting and screw on a shut off valve with hose threads on each end. That way you can use a smaller grey hose to get ride of your grey/yellow mixture. Remember to cycle your grey and black valves when the are covered with liquid so they wont stick closed from lack of use.
guskmg

[Wazbro]

Please realize some 70s AS had above floor black tanks. If this is the case with yours the 3rd valve will not work, water will come up in tub/shower before black tank is 1/4 filled. Also most would remove an above floor black tank to install composting toilet.

[JoleneAS]

Mine in a below-floor black tank.

I’m still having a hard time visualizing how people recommend using blade valves to link the tanks. I did a search here but not seeing anything with photos. Anyone have any threads they recommend for visual aid?

[TheGreatleys]

Originally Posted by JoleneAS

Mine in a below-floor black tank.

I’m still having a hard time visualizing how people recommend using blade valves to link the tanks. I did a search here but not seeing anything with photos. Anyone have any threads they recommend for visual aid?

It's pretty simple. You add a valve at your sewer outlet that you can close. You can see mine in the attached picture which is permanently glued on, but Valterra sells a twist on valve for this purpose here:

https://www.amazon.com/Valterra-T58-...dp/B000BGHYJS/

With the waste valve closed, you open both your gray and black tank valves so they empty into the waste manifold. But since there's nowhere for the water to go with the waste valve closed, the water in the two tanks will simply equalize until both tanks are full.

To dump the whole shebang, connect your hose to the waste valve and open the valve.

[rmkrum]

Note that this valve arrangement will work well IF the black and gray tank are installed at the same level in the frame of the trailer.

Trailers with an elevated black tank, where the toilet sits right on top of the tank will fill the gray tank first, and possibly not fill much of the black tank, or have tank contents come up in the shower drain...connecting the two tanks in this scenario will not gain much tank capacity.

[JoleneAS]

Are there any options to interlink the tanks under the subfloor or is that less recommended?