RV Holding Tanks: The Ultimate Guide
By Kelly Beasley
Published: January 5, 2020
Last Updated: October 19, 2021
An RV is essentially a house on wheels.
No matter whether it's a travel trailer or a motorhome, it probably has every home need from sinks with running water to a furnace, to electricity, powered by batteries or a generator.
If one has a kitchen sink, a shower, and/or a conventional toilet, it also comes with RV holding tanks to store the water and waste you put down the drain.
Why? Because there are times when campers don't have utilities in a campground.
Some people want to camp on public lands or in areas or campgrounds that do not offer utility services such as water, power, and a sewer hole for dumping.
Therefore, almost all campers sold from a manufacturer have at least three RV holding tanks. A freshwater tank, a black water tank, and a gray water tank.
They store the water you will need when dry camping and provide a way to keep the used/dirty water before you dump it at dump stations.
Thankfully, our society prohibits dumping sewage or otherwise dirty water just anywhere, especially on our precious and fragile public lands.
Let's look a little closer at these camper holding tanks and what they do.
Fresh RV Waste Holding Tank
The fresh water tank is for dry camping (when you aren't connected to utilities).
You won't be connected to a water supply, so you must bring your fresh water supply with you when you go camping.
There is no standard size of camper water tanks. Instead, your water tank capacity could range anywhere from 10 gallons to 100+ gallons.
That said, your fresh water tank is usually the largest of all of your holding tanks for RVs.
To fill, use a 'potable water' hose (usually colored white for easy identification) to fill your water tank at any potable water spigot.
You can find these at gas stations, dump stations, campgrounds, and other similar places.
Is It Ok To Travel With My Water Tank Full?
Yes, it is OK to travel with your fresh water tank full. RVs are designed to carry the weight of a full water tank while on the road.
Otherwise, what would be the point of having one? Many destinations don't provide water, so you MUST bring your own.
That said, be sure you KNOW the actual weight of your RV when it's full. Do not go past the allotted weight the manufacturer says it can handle.
If you are very close to it, you could be over when you fill your water tank. It's best not to be close at all for maximum driving or towing performance.
Grey Water Waste Tank
Next, your RV likely has a separate grey water tank.
After fresh water is used for the sink or shower, it drains down into your grey camper waste holding tank where it's held until you dump it. This camper waste tank holds everything but sewage.
That said, some very small RVs don't have a grey dump waste tank. They only have an RV sewage tank.
In this case, the water from sinks and showers then goes into the black tank.
Your grey water tank captures sink and shower water. Meaning it's nasty and stinky.
Pro Tip: Be sure to let as little food debris go down your sink as possible and into your RV waste holding tanks.
Black Water RV Holding Tank
The black water tank is the nastiest and the scariest of the three types of RV holding tanks. It can induce the fear of God into even the biggest muscle truck guy around.
NO RV owner in their right mind wants to have a spill from their black water tank at the dump station.
Why? Because your black water tank is your RV sewer tank! YOU MAKE SEWAGE, and it goes down the facilities and into the trailer septic tank.
It should stay ONLY in the tank or go through your sewer hose.
It's downright disgusting, but it's also a necessary evil. (Even if you have a composting latrine, you still have to dump. You have your grey RV wastewater tank to dump at the dump station.)
How Does A Camper Septic System Work?
A camper septic system works by simply acting as a holding tank for your sewage. It's not a SEPTIC TANK that works like at a house.
With an RV septic system there are no leach fields, no breaking down needed (not really), none of that. It holds your sewage until you dump it. That's it!
You go in the toilet, then flush. The water and your contributions flow down a tube and into your tank, whatever size it may be.
Water you use in the shower or sinks goes into a separate holding tank for RV use.
All the waste water stays in the trailer holding tank until you open the corresponding valve to dump it. This is what RV septic systems do.
How Big Are RV Septic Tanks?
RV septic tanks will come in a multitude of sizes, ranging from 10 gallons to 100+ gallons. Generally, the bigger the RV, the bigger the septic system for RV will be.
Travel trailer holding tanks will generally be smaller than motorhome holding tanks because trailers are usually smaller than motorhomes. Also, motorhomes are typically equipped to carry heavier weights. (Full holding tanks for RV use are heavy!)
How To Dump Your RV Holding Tanks
Dumping your RV holding tanks is a simple process, though scary the first few times. Find a dump station. Park so your holding tanks outlet is near the sewer hole.
Connect your sewer hose to your RV and to the sewer hole. Open your camper sewer tank black valve first.
Once done, close the black water tank valve. Now, open your gray water valve.
After the camper waste tanks are drained, remove the RV end of the hose and rinse it out with the water supply.
After letting most of the water drip out, remove the end from the sewer hole and put your sewer hose away.
MAKE SURE you closed off both valves, and you're done with the dump station!
How Often Should An RV Septic Tank Be Emptied?
How often an RV septic tank should be emptied has everything to do with tank capacity and how many people are using them, as well as how conservative you are with water usage.
A huge determining factor as to how long until you need to dump your camper sewage holding tank is how often, and how long, you shower. The shower is by far the biggest single contributor to filling up your camper waste water tank.
I, Kelly, can go about 3.5 weeks if I don't ALWAYS pee in my black tank and if I sometimes throw non-contaminated water outside instead of allowing it to go down into my grey tank.
Some people must dump their RV wastewater holding tanks once a week or more frequently. It would be best for you to learn your habits and your RV in order to answer this question correctly.
How Do I Clean My RV Holding Tank?
You clean your RV holding tank based upon which RV dump tank you are wishing to make sure is cleansed. The black RV sewage holding tank is the grossest to clean, but the fresh water tank is the most critical (since you often drink the water from this tank).
There's not much maintenance needed for your RV sewer tanks. Probably the fresh water tank needs the most. We'll come back to fresh water tanks below.
Meanwhile, the black and gray water RV holding tanks can sometimes have issues.
Let's start with the black tank part of the RV septic system.
Performing an RV black tank flush is a great way to limit the number of issues you'll have. Read on to learn more about what to do with this waste holding tank.
Black Tank Maintenance
The most significant issue with your septic tank for RV is clogging.
This is NOT what you want to happen. Your tanks can clog in one of three ways:
- Too much toilet paper and not enough water.
- Using non-septic friendly toilet paper.
- Unintentionally building a "poop pyramid" in your RV poop tank.
All of these RV waste tank issues are largely avoidable.
How To Avoid Black Tank Clogs
Secret #1: First and foremost, we recommend NOT putting your TP down the toilet. You will never have an RV septic tank clog if you do this.
Secret #2: Not a fan of that idea? Then NEVER use non-septic-safe toilet paper. OR shred what you have before you use it. Just splitting up a line of TP into three smaller ones will help.
Secret #3: Last, NEVER keep your black tank waste valve open while hooked up to a sewer at your campsite. If you do, you'll allow the liquids to drain out immediately. This leaves the solids behind, and they will collect where they land. This is what is called a 'poop pyramid'.
Poop pyramids eventually block the drainage of your camper septic tank.
What Can I Put In My RV Septic Tank?
You can put three things into your RV septic tank (black water from the toilet): Poo, pee, and septic-safe toilet paper.
Putting anything else into your toilet is ill-advised, such as tampons, baby wipes, diapers, etc.
The gray RV waste water tanks will hold what you put down the shower or sinks. It is advisable to not allow food waste to enter your RV waste water holding tanks and to use environmentally friendly cleansers (soaps, shampoo, etc.). This minimizes the smell from your RV sewer holding tanks (gray water specifically).
Grey Tank Maintenance
Your grey camper dump tank shouldn't need much maintenance at all.
The worst that can happen is it springs a leak or drops out from underneath your RV. However, this is rare. (It HAS happened before!) Hopefully, the worst that happens to your tanks is a foul odor.
Keep in mind that these tanks and the pipes leading to them work just like your pipes at home. Your RV sinks have 'P' traps that hold water in them, so the grey tank smells cannot get inside your RV.
Therefore, if you are experiencing odors, check your 'P' traps first. There might be a build-up of gunk in there needing removal.
The other thing that might be wrong is your vent could be stopped up.
In the 5.5 years full-time RV'd, I've never had to do anything to my gray tank except clean out the 'P' traps.
Learn more about RV grey water tank cleaning.
Fresh Water Tank Maintenance
This tank stays pretty clean for the most part.
Especially if you use a filter every time you fill. There are a few things you can do to clean and sterilize this camper tank.
Can I Put Bleach In My Holding Tank?
Yes, you can put bleach in your fresh water RV holding tank. In fact, this is the recommended way of cleaning (sterilizing) this holding tank. BUT, you must flush it all out before using any of the water!
The general rule is to put 1/4 cup of bleach for every 15 gallons of water you put in to sterilize.
You will never be able to scrub out the inside of your tank. However, there are treatments on the market designed to sterilize the fresh tank and pipes leading from the water camper holding tank.
It's best to use a water hose you only use to fill fresh potable water.
If you use the hose you rinse out your sewer hose with, well, you can imagine that it can contaminate your fresh water. This is not recommended.
How Do I Check The Water Level In My RV Tank?
You can easily check the water level in your fresh water RV tank by using the tank monitor panel. Your RV likely came with a monitoring panel that show you the level of all of your RV holding tanks.
Push a button, and it will tell you approximately how much water you have. Depending on the monitor panel, the measurements will either be in thirds (empty, 1/3, 2/3, full) or quarters (empty, 1/4, 1/2, 3/4, full).
If you are fortunate enough to have a more accurate system, measurements will be in percentage of tank capacity.
There will also be buttons to measure the levels of the camper waste water tanks. Keep in mind that the gray and black sewage tanks are notorious for reading inaccurately due to buildup on the RV tank sensors.
When it comes to holding tanks for campers, typically only the fresh water level reading will be accurate after a certain amount of use. Unless you have the type of system that reads in percentages, as this uses a different sensor technology that doesn't get clogged like the cheaper (and more prevalent) sensors.
How Do You Deodorize An RV Holding Tank?
To deodorize an RV holding tank, you need a tank treatment. Yes, your black RV tank might emit sewage odors. This is less than ideal.
Most often, this happens when your rig is in scorching environments. (The only time I needed a black tank treatment was when I was in Florida in the summer.) Heat tends to make a travel trailer waste tank a bit on the pungent side.
As an RV owner, if this happens to you, get yourself one of a few products. They are treatments for RV tanks.
We like Happy Camper or Tank Techs RX for your RV tanks.
These products have enzymes that break down solid waste and eliminate odors.
Specifically, Tank Techs RX can keep everything clear so the sensors on your camper waste tanks don't eventually get covered by Struvites.
Struvites are naturally occurring in septic systems and create hard deposits that cause your sensors not to read correctly.
These products used in the grey tank combat odors in any motorhome or trailer septic system.
Do I Need An RV External Holding Tank?
You only need an RV external holding tank (also known as an RV portable waste tank) if you need to dump at a distant dump station before you want to move your RV.
There are many brands available, some better than others. (See the RV portable waste tank reviews.)
These portable waste tanks allow you to dump into the external tank and then transport that tank to a proper RV sewage system dump.
I've never used one in my 5.5 years of full-time travel, but if you're stationary, more often than not, it might be good to have an external camping waste tank. Especially if the places you stay don't have sewer hookups that allow you to dump your RV directly into the ground without moving from the campsite.
In order to use your RV holding tanks without issue, there are a few key things to know about them.
Mostly, you should follow rules for your black tank so it doesn't get a clog, and make sure to occasionally sterilize your fresh water tank.
Holding tanks for travel trailers and motorhomes must be dumped when they are full or close to full. You do this at any dump station or other approved waste facility.
Figuring out your RV holding tanks isn't rocket science, but yes, you should educate yourself about a few aspects so they keep working as they should.
Don't be scared, just get out there and start using yours. You'll figure it all out as you go.
Learn something from this article? Yay! Learn more about RV basics on Camp Addict.
Author: Kelly Beasley
He-llllo. I'm the co-founder of Camp Addict, which my biz partner and I launched in 2017. I frigging love the RVing lifestyle but in December of 2020, I converted to part-time RV life. Heck, I lived in my travel trailer for over 5.5 years, STRICTLY boondocking for pretty much all of it. Boondocking is a GREAT way to live, but it's not easy. Anyway, I'm passionate about animals, can't stand campgrounds, I hardly ever cook, and I love a good dance party. Currently, I can be found plotting and scheming whether or not to start collecting farm animals (or plotting my next RV trip!) at my beautiful new 'ranch' named 'Hotel Kellyfornia', in Southern Arizona.