Reusing Greywater in an RV


I’ve read once that RVers “camp” differently.

RVers are said to pull up, plug in, and stay inside their air-conditioned and satellite adorned rigs until it’s time to go. I don’t know if that’s true for some, but it’s certainly not the case for us. We believe, strongly, that we live outside. The bus is where we cook, and where we sleep. Usually though, we eat and read and “do school” and hang out, outside.

This isn’t always the case, however.

Last year, we found ourselves in a city where the only place to park was a casino parking lot. This was the perfect place to hide inside and avoid the hustle and bustle of cars, tractor trailers and RVs coming and going. And it’s worth mentioning that the heat index was 105°. Yes, one hundred and five.

I’m fine with hiding inside. The kids were not.

Like soda from a can that’s been vigorously shaken, they violently explode out of the bus door at every opportunity. I found myself outside, frequently, yelling for them to come back in and for heaven’s sake, put some pants on.

In order to facilitate our (often pant-less) outdoorsy-type camping, we need to be able to park in nature. Parking in a casino parking lot, or indeed in a grocery store lot (which we have done, twice, the police came…it’s a story for another day), doesn’t work well. We like to boondock, out in the woods, preferably not within sight or sound of others.

a coach bus converted to an RV parked at a brewery
Parking at breweries definitely counts as boondocking.

We like to drive down a dirt road and find a spot under the trees. To get lost in nature. To sleep with the windows open, listening to the sounds of owls and crickets. But, as you know, this presents a new set of challenges. How do we live in the woods without those absolutely necessary full hookup sites? Luckily, we knew what type of campers we would be when we built the bus, and designed our DIY RV to facilitate long off-grid adventures.

an RV camping off the grid near a teepee in Arizona
Off grid RVing in Arizona.

Like many others, we have solar panels on the bus roof which magically provide almost unlimited electricity. For now though, let’s ignore the solar setup, the pant-less children and the parking lot police, and focus on another essential element of the equation: water.

When converting our charter bus, we initially installed two tanks to equal 100 gallons of fresh water. We don’t typically drive around with all that water weight, and it’s actually rare that we fill our tanks completely unless we plan to be off-grid for awhile. We’ve filled the tanks at some obvious locations (campgrounds, friends’ homes) and at some of the most random of places (churches, gas stations, fast food restaurants). Once equipped with 100 gallons of fresh water, we can last for a looong time. Some estimate that the average American uses 80-100 gallons of water per day. It probably goes without saying that all of us road folk don’t fit neatly within the confines of “the average American.” If we are extra cautious, our family of six can get by on about 5 gallons per day, or about 15 if we shower.

Did you know that one of the largest uses of water in that average household is flushing the toilet?

Many travelers have circumvented that by opting for composting toilets. Our own personal decision was that a composting toilet wouldn’t work for us. For many it does. We decided instead on an RV toilet. But given that I couldn’t bear flushing away that precious fresh water, we decided to hack the system and design something that would work better for our family. That is the whole point of a DIY conversion, right? To make exactly what you want? So, if a composting toilet doesn’t work for us, and we need to consume as little water as possible in order to stay wild, what’s a family to do?

Our decision was to use an RV toilet, but to alter the plumbing so that it uses gray water to flush, instead of fresh.

a composting toilet in the bathroom of a vintage airstream

Compost Toilets: Are they good for travelers?

We have lived for years at a time without a toilet. Or, perhaps more precisely, without our own toilet. For the ten years or so we’ve been traveling, around half of that time has been spent living out of a van, and a van only. We never bothered with installing a shower, indoors or out, […]

The premise is not new by any means but we didn’t know anyone who’d done this in a conversion so we kind of made it up as we went along. The benefit for us is two-fold: on one hand we aren’t flushing precious fresh water down the commode and furthermore, we have a way to divert some of that gray water that we create by washing hands and dishes.

I’ll explain our set-up but first, a small disclaimer: my husband and I are not plumbers, nor do we play them on TV. This entire system (our whole bus conversion to tell the truth) are DIY and work for us, not necessarily for you. Now that we’ve gotten that out of the way…the magic begins with our two fresh water tanks equaling 100 gallons. We run water into them through those fancy hose-attachment RV filters. Our bus was a Greyhound in a past life and we specifically chose it because of the storage bays located underneath the bus. All of our tanks, pumps, most of the plumbing, and indeed the majority of the solar set-up (minus panels) live in those storage bays. Without those bays, you’d need to be creative with tank placement. I’ve seen under the chassis installs, tanks under beds and couches, you name it. So our tanks are in the bays and easily accessible and fillable. Next the water goes to our sink and shower with the help of a 12v pump. The water heater is a low-flow tankless, powered by propane.

a young boy working in the storage bay beneath a bus that's been converted into an RV
Getting to work in the storage bays.

Okay, now here we go down the drain. Both sink and shower are outfitted with fine mesh screens. This might not be as important if you are dumping your gray tanks but for us, clean(ish) gray water is paramount. Not seeing those tiny food bits again are very key to the success of this operation. Water flows into our 50 gallon gray tank where the chose your own adventure part begins. We can either dump our gray tanks as an RV does (and we often do when the opportunity presents) or we can reuse the water. From the gray tank, the water is pumped by a second 12v water pump into the toilet and finally into the black tank. Our black tank is also a 50 gallon plastic tank mounted under the bus in the storage bays.

Has this worked for us?

Absolutely! It’s not completely perfect however.

For one thing, the filter placed between the gray tank and the toilet was constantly getting clogged. While we did have a cut-off valve to allow us to easily access the filter to clean it, we quickly got sick of the exercise and removed the filter altogether. Problems have been fewer since then.

Additionally, that gray tank can sometimes get a little ripe. You know it’s a little disconcerting when the flushing of the toilet stinks more that the business of using the toilet. I can only assume it’s because of the length of time that the water sits and stagnates and the bits of soap, toothpaste and whatnot that mingles in. To resolve the odoriferous and offensive water, we will on occasion throw a bit of chlorine in the tank.

First, it was a cup of bleach or so after every gray tank dump. But that was messy and imprecise so we switched to pool grade chlorine tabs. Just a tiny bit goes a long way and helps to keep the smell at bay. The final downside (and honestly, this is so minimal) is the fact that we have to watch what goes down the drain. I mentioned the mesh screens but it’s more than that. In my house, with my magic septic system, I was infinitely lazy and could drain a can of beans or toss an old cup of milk into the sink. It’s a hard “no” in the bus. The last thing I want to do is pour milk down the drain, only to see it again in a few non-refrigerated days.


Hard pass.

This forces me to be more thoughtful about the ‘away’ part of throwing things away.

For those of you interested in recreating our setup, here is the general process of the build:

We started with 50 gallon plastic barrels that are pretty readily available. I think one came from the brewery where my husband worked, and the other purchased (for less than $20) from a farm equipment place.

two storage containers combined via a wooden frame
Building the frame for the grey and black tanks.
a diagram of the system, showing how the various components relate to one another
RV gray water recycling diagram.
all three tanks connected
The system as a whole.
Various components of the system.
Various components of the system.

Next, we determined placement. Basically the gray tank is directly below the shower and the black tank is directly below the toilet, making for easier plumbing. A frame holds the very heavy water-filled round barrels in place and keeps them from rolling around. Marty purchased dump valves from Amazon and installed them on each of the barrels using uniseals. This allows us to dump gray and black at any RV dump station. A critical error was made here – the black tank is on the passenger side of the bus, which is not standard. RVs always have their tanks on the driver side. This means that sometimes the bus has to drive into the dump area backwards so that we can connect the black tank.

Don’t make this mistake!

It’s not worth it for us to fix it, but it does make things a little more tricky so please learn from us. Marty installed a one-way check valve so that, if we choose, we could dump the gray tank directly into the black tank. We have done this exactly once (to test it) this but I guess it would be beneficial if we ever hook up to a sewer line – we can just feed the gray water into the top of the black tank and connect that single tank. All plumping is S or P trapped, depending on space, and the black tank is vented with a Sure-Vent.

the system, including a large blue plastic container, check valve and pipes going in and out in order to recycle the grey water for flushing the toilet

The system I’ve outlined above easily allows us to roll into a forest for three or more weeks. We can extend the time out in the wild by bringing fresh water back to the bus – sometimes just a few gallons at a time. Our off-grid record is 47 days straight, although I distinctly remember that we did dump the tanks at a random RV park when we were moving from one spot to another. So that’s 47 sequential days that we didn’t plug into an electric, water or sewer hookup, not 47 days in a single spot.

Moving gives us the opportunity to dump the tanks and replenish fresh water at the above mentioned random spots. I think the longest we’ve been completely stationary is about three weeks. The black tank can last longer than that but I’m not interested in pushing it’s limits.

For us, a bus conversion equals freedom. It’s freedom to explore the parts of the country that we wish to see. Freedom from RV parks is important to us too. An off-grid life, the ability to boondock where we choose, plays a really big part in the equation. The solar setup and the water usage allow us to stretch each precious visit for just a little longer, and to allow us to focus on our family, and not on the everyday basic needs of a road life. The simple change of flushing with gray, instead of fresh, allows us to stretch our time just a little more and to feel better about our family’s water usage. If we build again (whether a conversion or a house), I imagine we’d try to capture and reuse gray water much as we have done with this bus.