Use grey water to flush RV toilets

Ok, this idea will make no sense to those who have not gone RV camping. RVs have 3 water tanks -- one for fresh water, one for the toilet sewage (known as "black water") and one for the other drains (shower, sinks) known as "grey water." When you camp in unserviced campsites for a while you become very aware of the capacities of your tanks.

However, the RV uses the fresh water tank to "flush" the toilet. It seems to me that with a small extra water pump, one could use the grey water, or a mixture -- grey with a final spurt of fresh to rinse the bowl.

RVs don't really flush the toilet, that would use way too much water. You rinse the bowl after #1 and you pre-fill the bowl before #2 and rinse later. Yes this requires an extra pump, and since you can't draw from the very bottom of the grey tank, which has some sludge, you even need access to both pumps which perhaps makes this too complex, and thus explains why it isn't done. And the surplus of "free" water might make you overfill the black tank, which is sometimes your limiting tank. And perhaps if you are going this far you should make the jump to a propane powered composting toilet.


I am interested in comments (pro or con) from people who own stand alone composting toilets.

I am NOT interested in testimonials from the manufacturers.

Dear Brad,

How will I know if anybody responds?

If you create a userid on the blog (or use any other userid in the drupal system) it offers you the ability to subscribe to a thread, and get E-mails when comments are posted.

I use grey water exculesively to flush my rv toiet on long, remote trips. I installed a side input into my grey water tank 1/2" above the bottom of the tank towards the rear of the tank w/ a simple water filter followed by a demand pump in the line. When setting up, I simply make sure my rv is sloped one degree or so downward toward the rear. I have a valve, just under the edge of the trailer which branches to the grey or fresh water feed. When valved to fresh water, the extra pump is unnessary. (So that if you have full hookups or are on a short weekend trip it is unnecessary to tap the grey...The systems works great, you just learn very quickly not to pour things like coffee, soda, etc down the sink. They have a tendacy to return to the toliet rather stinky (the key is too limit sugars and protiens). Do that, with the filter, you wont know the difference.. After using this system quite extensively on my rural property, it is very easy to go a couple weeks without dumping. (using the outside shower...) I have a gravity feed spring, so fresh water is not an issue, only dumping...

has anyone heard of a commercial system that will recycle/filter the grey water for you? do any r.v.s come with this technology? thanks!

I was just wondering about this today which was what led me to this page. In many areas, Car Wash's and Laundromats are required to recycle their water, so I would imagine that some system could be devised on a smaller scale that could be installed in a motorhome or trailer. The task of flushing and refilling your water tanks is a real pain and the ability to recycle your gray water would extend the maintenance interval on your tanks considerably as many water uses could be done from your gray tank rather than your fresh tank. I wouldn't drink or cook with water from the gray tank, of course, but for toilet and wash down purposes it would save a lot of water and maintenance over time.

After using grey water recycling for many years in my RV I decided to market a series of products that focus on RV water conservation and reuse.
The first set of products are focused on grey water recycling.
--We have a book that discusses this topic and provides the in's and out's for safe RV grey water recycling.
--We also have a Dry Camp Days calculator (a sophisticated MS-Excel workbook) that allows you to enter your tank sizes and your water consumption habits then it calculates your without recycling and with recycling benefits. It includes a consumption analyzer engine that will provide customized recommendations on how to extend your Dry Camp Days.
--Also available is a set of parts kits that include everything you need for grey water recycling including a custom manufactured bulkhead blind tank fitting. This allows you to easily and quickly tap into your grey tank from the outside only. It creates a extremely secure and water tight connection with just a 1" drilled out hole.

Go to to learn more. If you would like to discuss further, go to the contact-us page on the web site and leave your questions and I will get back to you ASAP. Or you can email me at

You really can extend your Dry Camp Days by 75-90% with grey water recycling.

Will be setting up a camp at the lake and will not have water or sewer. The chem toilet or portapottie will work and have to be dumped or a portajohn service used. The problem will be showers and the grey water and what we can do there. Any suggestions? The lake assoc. and town are very strict. Please email with your ideas. WE are used to camping with an RV and Sewer system.

We're planning on buying a small RV soon and I didn't realize until reading your blog post that RV's don't use the grey water for flushing.

It makes so much more sense. When we finally get our RV I'll be making this modification.

Thanks for the inspiration.

I have been reading about graywater recycling systems for homes, and am thinking about a scaled down version for an RV, as a way to safely dispose of graywater without a dump. I find I'm often in a position to get water but dump stations are much more rare. Some ideas:

> Wash the RV with the graywater (using biodegradable soap would be a nice idea on this one)
> Filter the graywater with a sediment filter to catch hair, food particles, etc. then use a mini soil leachfield (perhaps a large potted plant or two) to filter the water then pass it out the bottom on to the ground or storm drain, or use it to water any nearby plant life)
> Boil it, distill it, treat it--then you can reuse it over and over for washing (the RV), flushing, etc. whatever you feel comfortable with. But you'd need a 4th tank for "white" water... treated gray water to be used for certain things.

I'm wondering how I can test white water to see if it's clean enough to legally use in a way that discharges it on the ground, i.e. washing a vehicle, watering plants, etc.

ideas and thoughts on any of this?

- B

I'm concerned about Cross contaminations, to prevent any contamination from gray water back into fresh water system.

I am interested in learning more about gray water systems for use near waterfront cabins, and in RV's. I've seen other precautions such as in commercial kitchen drains where there is a in the pipe with a funnel like fitting below to drain sink without bacteria being able to follow back up drain into sink, and new anti-siphon valves on water campground/public water systems to protect the siphoning back into the water system from a possible hose sitting in a contaminated puddle etc. from being sucked back into the water distribution system to cause someone else to be sick.

So I too will be interested in hearing more. And yes I know that some safety features just protect us from ourselves, when most people can follow safety precautions.

I am looking to learn safe gray water disposal/recycling systems, to reduce septic system use. I've heard that under use of septic system can cause issues. (I still have a lot to learn).

Listen to my idea,
I believe allmost all the water from your RV can be recycled/treated and reused possibly in any way you choose.
Here is my idea.
Why can't we find a way of useing a dehumidifier to draw the evaporated moister out of our systems and use and reuse it?
I now use a dehumidifier in my bedroom every day and it upsets me when I dump a gallon of water away every day,just seems like a way can be improvised to draw the humidity back out of all water based things we use to make it possible to be used over again,isen't that what they do on the space station and shuttle?
Make a dehumidifier that is small enough to run off a solar panel by day and batteries or land line at night.
Gotta be a way.
And why can't a gutter of some sort be put on Rv's to catch rain water with a tank to catch it and filter the rain water and pump it back into the fresh water insted of letting it all run on the ground?

While there are some systems for this, primarily fog and dew harvesting, dehumidifiers (which are essentially refrigerators) take a lot of power, so they are not really that practical as a water source unless you have tons of power around, or a very humid climate.

Would that be possible to have a larger holding tank for black water on most motor homes, as they usually come already installed; pretty much as about 40 gallons of Black and around 60 of gray on large RVs, without major modifications on the system?
And to possibly have a second gray water holding tank connected to the dump system. like lets say 15 gallons extra holding tank, so one could set up a drain near the sink and dispose of gray water with lots of oil, grease, leftovers, rest of soda, milk, coffee and the like?
If one is using gray water for flushing then the amount of water in the first gray tank would supposedly be decreased and if water from it after passing through filtration is almost as good as clean then one could just water the lawn around the RV when the gray tank gets full?

I am not so sure how long a black holding tank can keep waste in without taking a trip to the dumping station as I just went RVing very few times on weekends. Could someone shed some light on this for me?

Bigger tanks are of course possible, but they take precious physical space, and when full they are quite heavy. They must be in the bottom -- the black water tank is almost always located directly under the toilet and the gray typically under the shower. 80 gallons of water weighs 640lbs, which is not trivial.

And yes, you want to empty the tanks sooner rather than later because they stink, especially the black one. No matter how many chemicals.

I'm surprised I don't see more dry composting toilets running on propane or something which would change things a bit.

How long can a holding tank for black water go without a trip to the dump station before it starts to stink?

But it's minor and you leave the vent open in the bathroom. It also depends on how well your toilet seals. If you go driving and slosh it around, it's worse.

In my family we always put ~2" of water in the toilet (not enough that it would slosh out) so the liquid removes any chance of smell coming through. It also has a vent to the roof so pressure can't build up (and cause a bubble to go through the liquid). Works great and we've never smelled it except once when we overfilled it (when we were still new to RVing and didn't realize how inaccurate the sensors could be- still read as 2/3).

Dehumidifiers will only work well on ambient that is very humid and will not do well in dried places. Besides being expensive to work them there is also the question that viruses, principally fly, spread really well on dried and warm environments.

Sorry for the typo, I meant FLU and not fly.

You can use it to flush toilets for sure but I would think you’d need lots of extra black water storage for extended stays. Our problem on extended stays was always filling the black water first.

We just have a simple strainer and connect the grey water to the pressure washer and use it to wash our motorcycles (at the MX races) and the outside of the motorhome. I also use it with some soap for doing laundry in a bucket with an old fashioned Plunger Washer, then rinse with fresh water in the bathtub and hang up outside.

We do multiple things I sometimes carry a portable wheeled 30 gallon waste water tank. On shorter trips we leave it at home. The new Motorhome I'm building doesn't have a flush toilet or black water at all and we just use a built in version of the Pett Toilet system, and instead of their expensive gelling "poo powder" we use cheaper Gelling Kitty Litter. Since the bulk of our camping is "Boondocking". We all like this system much better never any black water to even think about and no sewer hoses and all of that, just a smaller one to dump the grey water that doesn't get used washing everything.

Then if there isn't a dump site at the Race track we wheel it to the back of the motorhome and use the lift gate to put it in the Toybox garage until the next RV dump site and dump it and the Motorhome tanks. We also carry a portable bucket type toilet and use the gelled kitty (again like the Pett System) liter one scoop per use then throw it out with the rest of the garbage. We also use the public outhouses Etc as much as possible.

Some other things is I've installed two extra 30 gallon fresh water tanks now when we go down the road we fill one for road use. Then before pulling off to camp we fill the other 30 gallon tank and the 60 gallon factory tank. Also we carry all of our drinking water under the dinette in 1 gallon jugs. And I have four 7 gallon jugs of fresh water that we use to anchor the awning with motorcycle tie downs and climbing carabineers until we need them.

Useing all of these measures we have dry camped up to 5 days with up to 8 people. Everyone had enough showers and all this may be a bit unusual as we have the Toybox and the constant need to wash motorcycles. So I haven't seen the need to add using the grey water for flushing. We just have a very clean Motorhome and motorcycles!

Gerald Fuller

I simply take minor offense at the comment "this idea will make no sense to those who have not gone RV camping."

I'm in the "learning before I leap stage."

But it occured to me "why is my kitchen rinse water not good enough to flush a toilet with."

That thought led me to this page. So give us 'virgins' a break... literally. Some of us simply need "broke in," that's all... we know the mechanics! hehe

I seriously didn’t have any idea about these RV camps. I am happy that I indeed got a lot to learn a lot from this site. Anyways keep sharing the updates that would improve camping experiences. I would like to know more.

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