RV Septic Tanks: Everything You Need To Know
(Camp Addict does NOT accept payment from any company to review or endorse their products.)
RV septic tanks are the part of your RV's plumbing system.
They hold the waste water that goes down your sinks, toilet, and shower.
Waste tanks allow an RV to be self-contained, storing gray water and black water until it can be dumped at an appropriate sewer connection.
As simple of a job RV holding tanks have, there is a bit to learn about their proper use and maintenance.
This includes the 'fun' job of dumping the tanks.
Read on to learn everything you need to know about an RV septic tank, and probably some things you didn't know you need to know.
Learning About RV Septic Tanks
We think you will agree with us when we say: "The black water tank is probably one of the things newbie RVers fear the most about using their RVs."
Don't worry- we are here to teach you how they work. Once you understand them a little more, you will realize they are pretty simple.
You will probably wonder what you even scared about before. Let's get down to it.
Gray Water Tank Explained
Your camper gray water tank is where any used water EXCEPT your RV toilet waste water goes.
It's the water that goes down your sink drains and your shower drain. Shower and sink water ends up in your gray water tank.
Most motorhomes and smaller travel trailers have a single gray water tank.
There are dual gray water tanks usually only when the kitchen sink and the bathroom sink are far apart from one another.
Having two gray water tanks also usually means you'll have to drain each waste tank separately (they'll each have their own drain valves).
Black Water Tank Explained
Anything that goes down the RV toilet ends up in the camper black water tank.
However, it is the 'scarier' of the two types of waste tanks for two reasons:
- Sewage! It's pretty disgusting if it spills. Spills can and will happen. Ask any seasoned RVer! Don't worry, you'll get through it.
- It clogs easier than the gray water tank. The black water tank has solids (toilet paper) in it. The gray waste tank generally does not (except for food particles). Therefore, a waste tank with a lot of toilet paper (or the WRONG KIND of TP), or not enough liquid, can cause solid matter buildup or clogs.
Using holding tank treatments, using enough water, and using the correct type of RV toilet paper, or best yet, NOT putting any TP down the RV toilet, all can keep your RV septic system flowing correctly.
Should I Leave My RV Waste Tank Drain Valves Open?
NEVER leave your black water tank valve open 24/7 when you are connected to a sewer system hookup at a campground.
Because all of the liquids will flow out but the solids will not. You will end up with the infamous 'poop pyramid' and it will clog.
Always keep your valve closed UNTIL you go to dump the waste tank. Your black water tank needs to have plenty of liquids in it to drain solids properly.
You CAN leave your gray water valve open when hooked up to a sewage drain at a campsite (though it too is generally a good idea to let some gray water accumulate in your waste tank before draining to flush out any food particles).
Just never leave the black tank valve open!
RV Black Water and Gray Water Tank Sizes
How big are your waste tanks? This is something you will have to find out for yourself. The gray and black water tank sizes are not necessarily going to be the same.
Your RVs user manual will tell you how many gallons each RV waste water tank holds. Also, you can check for it online.
Usually, you can get your specs somewhere online by searching for the year, make, and model of your RV, or by checking the brochure archive at the RV manufacturer's website.
RV Waste Tank Sensors
Oh man, the notorious waste tank sensors.
If you know any full-time RVers, they will all tell you that you CANNOT depend on what your black water tank sensor says.
Your RV should have a monitor panel that should tell you the levels of your gray water tank, your black water tank, and your fresh water tank, as well as your batteries.
Your gray water tank sensor can, and might well be, accurate. Especially if you do a good job of not letting any food particles down the drain.
If there's nothing but waste water in the tank, there's nothing to stick to a sensor inside the tank to give it a false reading.
Though most probe-type gray tank sensors will eventually end up reading inaccurately due to soap scum or grease buildup.
If your monitor panel isn't reading accurately, it will eventually be obvious when your gray water tank is full because your sinks and shower will draining very slowly and eventually back up.
And if you wait long enough, a full gray water tank will back up to the lowest outflow point, which is usually your shower.
In other words, an overflowing gray tank will result in your shower pan filling up with gray tank water.
Yummy! The black water tank is a different story.
All of your 'contributions' that are not liquid matter have the opportunity to become stuck to the sides of your black tank.
#2 solids (human waste) and toilet paper can both stick to the wall or the sensor probes.
This will throw off a reading (when you have the typical probe-style tank sensors). Seriously gross, right? Deal with it.
It's what happens.
However, the more common reason probe-style tank sensors stop working is because struvites form inside the tanks, causing the sensors to read inaccurately.
See the below video for more information and learn more about what you can do about struvites in this section.
What Are Struvites?
If you can see down into your tank when you flush your toilet, lucky you. Your eyes are your best gauge.
Again, gross, but it works. It's the most dependable method of determining how full your waste tank is.
Otherwise, if you have an RV toilet where there is a curve in the pipe going down, you can't see into the tank. In that case, if your sensors aren't working, it's a matter of live and learn through experience.
If you know your septic tank size, you should eventually be able (and you had better learn this) to guesstimate how full your tank is.
Have fun with that, but you WILL get a feel for it after a while.
(Worse comes to worst, you will get to a point where the toilet will not flush anymore! But try not to get to that point of course.)
If your sensors are off, you can pay a professional tank cleaning service to do a thorough cleaning which may make the sensors work again (at least for a while).
RV Holding Tank Treatments
Have you ever stood in an RV supply store and stared at the giant selection of RV holding tank chemicals and treatments?
Did you wonder why there are there so many and which you should use? We agree that it can be overwhelming.
Here is a great primer video on the different types of septic tank chemicals:
RV Septic Tank Treatments Explained
Learn something there? We sure did!
Camp Addict co-founder Marshall did a test of TankTechs RX after living full-time in his Lance travel trailer for about 3 years, hoping to get his sensors reading correctly again.
He used TankTechs RX for around 6 months, hoping that eventually his septic tank sensors would clear up. They didn't.
In order to get Marshall's tank sensors working properly again, he would have to have his waste tanks professionally cleaned and then use TankTechs RX from then on (so the sensors don't get covered again).
Marshall is currently using the Happy Campers Holding Tank Treatment in his black water tank and occasionally uses the TankTech RX in his grey water tank in the hopes of keeping mold at bay.
Brand New RV Advice
If you have a new RV that uses probe-style tank sensors (most RVs do, unless you've got holding tanks with readouts that show percentages - not just the typical E, 1/3, 2/3, and F), then consider using TankTech RX from the beginning.
If their marketing is to be believed, your sensors should continue working. Marshall will do this if he gets a new RV.
You'd think that TankTech RX would be pricey stuff if it works as advertised, but it's actually cheaper than other waste tank treatments that Marshall has used.
Happy Campers Holding Tank Treatment
Happy Campers Holding Tank Treatment is what Camp Addict Marshall currently uses in his black water tank.
He has no complaints about it as it seems to do what the company says it's supposed to do.
Per the manufacturer, "There are nine trace elements and two heavy elements that make up a highly concentrated blend of minerals and micronutrients.
In layman terms, it is the good bacteria doing away with bad bacteria to eliminate odor and accelerate the natural decomposition of the waste.
It has the ability to work longer and stay odor-free in over 100° temperatures. All of this and it is still friendly to all holding tank systems and the environment."
Three Ways To Dump RV Waste Tanks
When it comes time to empty your RV's gray and black water tanks, you have three options:
- Campsite: You can dump your gray and black water holding tanks at your campsite if a septic system connection is available.
- Dump Station: You can dump your waste tanks at a dump station by driving your rig there.
- Portable Waste Tank: You can drain your RV's waste tanks into an RV portable waste tank, eliminating the need to break camp and drive your RV to the dump station. You only have to take the portable black water tank to the dump station to empty it.
You dump your grey and black water tank using an RV sewer hose. A 'stinky slinky'. Heh.
If you are at a campground with full hook-ups, you are set. Nothing to worry about as far as 'when' to dump your RV tanks.
Don't forget, DO NOT leave your black water tank valve open just because you are hooked up to a sewer connection!
You can leave your gray water tank valve open all the time when connected to septic if you'd like.
Consider waiting until your black water tank is mostly full to empty it. This will cause the force of the flow to be greater than if it were only 1/3 full. The greater force should guarantee that the solids get cleaned out 100%, as long as there is enough liquid in the tank.
Emptying Your Black And Gray Water Tanks
We know, we know. This is the SCARIEST part of RVing (besides driving, for some folks). It REALLY gets easy once you have done it a few times.
It's a very simple process with extremely uncomfortable consequences if done incorrectly.
We have been there. (Well, mostly Kelly has.) This is why we are giving you a step-by-step guide on how to do the deed.
You probably have a single septic outlet for both the gray water and the black water to empty out of.
Some RVs have two gray water tanks and each tank may have their own waste disposal outlet. Outlets usually look similar on all RV's, something like this:
You should also see two valves or levers - one for the gray tank and one for the black tank.
Where? Depends on your RV! They are on either side of the sewer outlet in the travel trailer photo above.
If you have a Class A motorhome (or even a Class B or C motorhome), they could be inside of a bay.
On travel trailers and 5th wheels, they are usually on the outside under the RV. Use your owner's manual to find them if it's not obvious. (It usually is.)
The two levers should be labeled - black and gray.
We're giving you a step-by-step guide on how to dump your RV septic tanks along with a great video by Gone With The Wynns on how to dump the tanks on a Class A RV.
Dumping RV Gray And Black Water Tanks
Step-By-Step Guide To Emptying Your RV Septic Tanks
Are you new to the world of emptying your gray and black RV septic tanks?
Scared about the exact steps to take? So was I (Kelly).
So we are laying it out for you.
Open up the section immediately below and we will walk you through the process of draining your septic tanks, step-by-step.
Open to get your step-by-step guide to dumping your RV septic tanks
Click here to download a printable version of the below checklist (PDF).
- Put on some disposable gloves. Trust us on this one.
- Get your sewer hose out and place it next to the septic tank outlet.
- Remove the cap from the outlet. NOTHING should come out at this time... unless you, or someone before you, accidentally left one or both of the valves open.
- If liquid comes out, you better close the valve ASAP! Once the valve(s) are closed, take a deep breath. Wait. That's a bad idea... move away from the area THEN take a deep breath. Don't worry, **it happens. (Man, are we funny!) Attach the sewer hose and continue with the regular directions. Clean up whatever mess you now have by rinsing the area the best you can. You'll be amazed at how fast the flies will find it.
- Connect your sewer hose to your RV's septic system connection.
- Place the other end of the sewer hose into the dump hole. Secure it by placing a rock on top or by letting the cover of the dump station 'hole' sit on top of the end.
- Start by opening your gray water tank valve just a little. This way, if there's a leak, it's much less nasty.
- Close your gray water tank valve after confirming there are no leaks.
- Open your black water tank valve and let it drain entirely. It's a good idea to go into your rig once it's empty and run some water through it (unless you have a black tank flush, then see #10 below) to get anything 'left' in the tank out. If you CAN see directly down into the tank, it should look as clean as brand new if you got it all out. Use a flashlight.
- If you have a tank flush, connect your sewer specific water hose to the flush system and let it flow into the tank for about 3-5 min while the black tank valve is still open. When you are finished, shut off water and disconnect sewer specific water hose from your rig.
- Close black water tank valve.
- Open your grey water tank valve. This washes the sewer hose out so there's not fecal matter in it and its less smelly. Always drain your black tank before your gray tank.
- When finished, close your gray water valve.
- Lift up the sewer hose from closest to the RV to get any leftover liquid out by letting it flow into the drain.
- Disconnect your sewer hose from the RV once you are sure most of the liquid is out. Lift the end high to ensure nothing comes out of your end and to make sure all liquid drains into the dump hole.
- Rinse the sewer hose inside and out with water before taking the other end out of the drain hole. If no water is available, well, this is why it's a good idea to keep a gallon of water in a storage bay so you can rinse the hose.
- Disconnect the hose from the ground hole and cover with lid or rock (either is usually there).
- Put your sewer hose back into storage. Make sure it's empty!
- PUT YOUR CAP BACK ON YOUR RV's WASTE WATER OUTLET AND MAKE SURE YOU HAVE CLOSED BOTH LEVERS. This is very important- crucial for your next dump so you don't have an embarrassing gross accident.
You're done! It seems like a lot of steps, but it WILL become second nature.
Camp Addict Co-Founder
True story: Just yesterday I had a minor accident while dumping my black tank in Moab, Utah.
It's my, uh, fourth accident I believe? (I am, by nature, NOT a very careful person.)
I was all hooked up, checked the hose connection to the RV, and let 'er rip. Nothing leaking at the RV end.
Then I looked back at the septic system inlet on the ground. To my horror (once again), full-on feces and urine were shooting out from around the edges of the hose where it connects to the 90-degree end connection.
Crap! That's the second time this hose has come apart. Since I am not a good double-checker, I think it's time for a new hose.
Kelly's words of advice: If your RV sewer hose ends are able to come apart, check them EVERY TIME you hookup to make sure the connection is secure.
The #1 Secret To Avoiding Black Water Tank Clogs
We have a fantastic way to keep your black water tank from clogging, AND to not have to dump your waste tanks as often.
However, some people will balk at this idea.
Once you are over the preliminary 'ickyness' of the idea and try it, you will see that it's not gross or bad at all.
What's The Secret?
Put it into a trash can with a bag liner.
It will NOT smell.
Or, well, if yours somehow does, put it in a bin with a lid.
Your black water tank is MUCH less likely to clog if you aren't putting toilet paper down into it.
Practicing this secret also allows you to use any brand of toilet paper you wish.
No more worrying about what brand you purchase.
No, you won't have a trash can full of brown stuff.
Simply put it 'face' down, and it just looks like a trash can full of kleenex or TP used to blow your nose.
Example below- this is Camp Addict Kelly's bathroom trash can.
(Yes, this is her used toilet paper. No brown to be found.)
It saves a good bit of room in your black water tank.
OR, you can stay in your spot longer by getting a portable waste tank.
You Have Been Schooled!
What a sexy subject, eh?
You now know the difference between a black and a gray waste tank.
You should understand why you need camper holding tank chemicals.
Dumping your RV septic tanks can be a scary thing at first.
We have been there.
Now you have a printable instruction set to take with you when you dump if you are still nervous.
If you have any questions, please read the comments below.
If your question has not been answered, ask in the comments and we will answer it if we can.
Only relevant/complete questions will be answered, so please be thorough.
We have likely been there and love to help our readers if answers aren't met after reading our guide!
Kelly Beasley is co-founder of Camp Addict and loves sharing her enthusiasm for the RVing lifestyle. As a full-time RVer since May 2015, Kelly's playful writing style helps make learning about the sometimes dull subject of RV products a bit more interesting.
Camp Addict co-founder Marshall Wendler brings his technical expertise to help explain RV products in an easy to understand fashion. Full-time RVing since April 2014, Marshall loves sharing his knowledge of the RV lifestyle.