The best RV grey water tank for a skoolie build depends on the freshwater tank size, how often the grey water tank can be emptied, and the space allowed where the RV grey water tank will be mounted.
In this guide, we will walk you through these considerations to help you select the best RV grey water tank for a school bus conversion.
We will also go through the 7 best RV grey water tanks for school bus conversions that can commonly be used.
Special Note: This article does have affiliate links. If you click a link and happen to make a purchase, we may receive a small commission at no cost to you. Thanks for your support – this commission helps us to continue educating the skoolie community!
Selecting the Best RV Grey Water Tank
The 3 considerations that are essential to selecting the RV grey water tank for a school bus conversion are:
- Duration Between Draining
- Fresh Water Tank Size
- Mounting Space
Let’s dive into each one of these so you can understand how you can take these into consideration when selecting the best RV grey water tank to buy.
Grey Water Tank Empty Frequency
You can also phrase this as: how often do you want to have to empty the grey water tank?
Most of us will say never… Unfortunately, this is one of those dirty jobs that come with skoolie ownership.
In estimating how often you will empty your grey water tank, you will want to have your ideal scenario in mind as we move into the next two considerations.
When Sarah and I answered this question, we started out with wanting to last around 7 days before we had to empty our RV grey water tanks. This would allow us to stay either out in nature or at an RV park for an entire week before we had to make our way to the dump station.
Usually, we see people striving to last 1-2 weeks.
Fresh Water Tank Size
Having the RV grey water tanks proportional to the fresh water tanks is ideal.
If possible, the best situation would be to have a fresh water and grey water tank size that are the same size. Although not all of the fresh water will turn to grey water and end up in the grey water tank, this gives the opportunity to ensure you can really focus on your RV fresh water tank capacity. Everytime you need to fill up the fresh water, empty your grey water.
If you end up buying a smaller grey water tank, you will need to monitor both tank levels at all times. You will most likely do this anyway, but you can worry less if the tanks are proportional.
However, your grey water tank size will most likely depend on the last consideration the most – mounting space.
Mounting Space for Grey Water Tanks
The most important factor for skoolie owners is primarily where to mount grey water tanks and the available space for grey water tanks to be installed.
Don’t get me wrong – the duration between draining your grey water tanks and your freshwater tank size are important factors to consider. However, you will need to be realistic on the space you have available for mounting your grey water tanks.
You will want to mount your grey water tanks underneath the bus in a safe spot where you can fasten it to the bottom frame rales of the bus and where you can also easily install the drain pipes.
We have a separate guide on How to Mount RV Grey Water Tanks on a Skoolie, which goes through two different ways we mounted our tanks.
In the next section, we go through another question you are wondering if this is your first time living in an RV and/or doing a skoolie build – how much grey water does a person actually use per day in an RV?
What Is Considered Grey Water?
Grey water in an RV is widely accepted to be water used for handwashing and showering.
What water is considered grey water is highly debated.
Some include both dishwater and urine into the grey water category. Others strictly consider dishwater and urine to be black water.
Either way, it is best practice to just dump your grey water into dump stations and you’ll be good with either opinion you may have.
Is Dishwater Considered Grey Water?
Although this is heavily debated, the safe route would be to consider dishwater black water. Only hand washing and showering would be grey water, as it will contain no true waste.
Whether you agree with this or not is all of our own opinions – which is why I said it is debated.
We personally consider it “dark grey” water, especially since food is biodegradable with most people using it in compost.
We also make sure to use non-toxic dishwashing soap to not spread toxic chemicals.
Is Urine Considered Grey Water?
Urine is not considered grey water, it is black water. If you are adding urine into your grey water, it would be considered black water.
With that technical description out of the way, we personally consider this also be “dark grey” water.
Again, dump into a dump station or properly dispose of your grey water in another acceptable manner and everyone will be happy!
How Much Grey Water Per Person Per Day in an RV?
One person will create around 2 to 6 gallons of greywater on average per day.
We test how much grey water we consume repeatedly and over the past 2 years this hasn’t changed much.
Here is a general list of how much grey water you may create on average per day:
- Washing Hands: 0.5 – 1 gallon
- 1x Shower: 3-4 gallons (3-7 minutes of running water)
Here is a general list of how much dark grey water/black water you may create on average per day:
- Dishes: 1-3 gallons
- Urine: 0.25 – 0.5 gallons
Skoolie Grey Water Tank Insights
We had no idea how much greywater we would use on a daily basis.
Turns out we fill around 11 gallons of dark grey water per day.
This is without showering in our skoolie, so only sink water and urine made it into our dark grey water tank.
In total, we have 49.5 gallons of grey water tank capacity right now.
We started with a 31-gallon grey water tank, which lasted us 3 days between having to empty it again. Way off from our desired 1-week empty frequency.
We do have an overflow pipe that runs up and over the bus frame rails and into other 31-gallon grey water tank the sink drains into. This was installed, along with proper venting, after some really disgusting situations occured. You can read about those on our 15 Worst Skoolie Mistakes article.
Each of our grey water tanks are mounted under the bus to the rear behind the wheels. Actually, we have one tank directly behind each one of our wheels.
Sarah and I have been considering adding in an even larger grey water tank that is in-between the frame rails to increase our capacity to over 100 gallons to accommodate all of our fresh water tank capacity so that we would run out of fresh water before needing to empty grey water. This way we could maximize our stay wherever we may be to the point of needing fresh water, so we can fill and dump at the same time.
Based on our experiences of mounting grey water tanks and working with thousands of people on their skoolie build configurations, below are the best RV grey water tanks for a skoolie.
Best Skoolie Grey Water Tank Options
Below are some of the best RV grey water tanks for skoolies I would choose based on different sizes of school bus conversions, the number of people potentially living in the skoolie, and the skoolie lifestyle desired.
Best Small Skoolie Urine Holding Grey Water Tank
Best Large Skoolie Urine Holding Grey Water Tank
(Installed on the Skoolie Livin Bus)
Best Skoolie Grey Water Tank for Weekend Trips
(Installed on the Skoolie Livin Bus)
Best Small Skoolie Grey Water Tank
Best Large Skoolie Grey Water Tank
Best 100 Gallon Skoolie Grey Water Tank
PIN IT FOR LATER
*This article may contain affiliate links, which means we may receive a commission if you click a link and purchase something we have recommended. Please check our full disclosure policy for more details. Thanks for checking out our website and for your support!