RV Black Water Tank: Your Questions Answered

Kelly Headshot

By Kelly Beasley

Published: September 12, 2021

Last Updated: November 12, 2021

Oh, the 'joys' of the RV black water tank. Actually, RV black water tanks provide very little joy.

They do give you the pleasure of being able to use your private bathroom while you're out camping.

Which is a VERY nice joy! But they also cause anxiety. Because if you spill... well, you can imagine.

That said, your RV black water tank is a camper septic tank for your porcelain throne.

And you cannot hold this human waste forever under your RV, nor should you want to. You're going to have to dump that sh** eventually!

Dump Station sign

There are occasional issues related to this black water tank. Sometimes sewage odors are emitted, though this is rare. (Though rare, Marshall uses a deodorizer in his as sometimes his black water tank smells.)

Kelly uses nothing and is 100% fine, no odors. Also, they can clog.

Additionally, the tank sensors will stop working. (Seasoned RV owners know that tanks sensors are typically a lost cause.)

That said, there are some things you should know about your black water tank to keep it running smoothly.

Let's dive in. Not literally. That would be horrifying.

But here are the most frequently asked questions about camper black water tanks.

What Is A Black Water Holding Tank?

A black water holding tank is used to catch and collect everything that goes down your RV toilet. It is used to store human waste until you are able to empty the tank at a dump station.

These black water waste tanks are almost always mounted under the RV belly (under the floor in the case of a travel trailer black water tank or between the chassis frame rails in the case of a motorhome black water container).

Holding tank

They call it the black water RV tank for obvious reasons. What it holds is dark brown. I guess they didn't want to call it the brown tank. The other waste tank is referred to as a grey water tank.

Grey water tanks hold everything that goes down sink and shower drains. This water tends to be more grey in color, thus the name.

So black more accurately represents the color of sewage (GROSS!). So it should be pretty easy to remember which is which!

The tank is secured to your RV, and, barring any freak accidents, it will stay there and not fall (I've seen one fall off! It can happen).

How Does An RV Black Tank Work?

An RV black water tank works by catching and holding everything that goes down the camper toilet. It holds it until you open your black tank valve and dump the contents into a dump receptacle.

This enables you to use the bathroom in your camper for hopefully at least a week if you are dry camping (not connected to a sewer outlet).

Conversely, the gray water tank captures all that goes down the drains in your RV.

After it fills up, you're going to have to take care of it by dumping the contents into a dump station.

Waste Master hose in use

What Happens When The Black Tank Is Full?

When your black tank is full, that means it's time to dump the tank! Do this once it's full or close to full.

Otherwise, you could have an overflow situation on your hands, which you DO NOT want.

As horrifying as dumping an RV black water tank sounds, it's not that bad.

But yes, you must either rely on your tank sensors, or learn to know what it sounds like when the tank is almost full.

When a tank is almost full, when you go to flush, the toilet will make a 'burping' sound. You'll learn to recognize it quickly!

It's best to learn approximately how long you can go before you need to dump instead of relying on unreliable tank monitors.

How Often Does A Black Water Tank Need To Be Emptied?

How often you need to empty your black water tank depends on the size of the tank and the number of people utilizing it. My black water tank is about 20 gallons.

As a single female, I can stretch my tanks to about 3.5 weeks if I don't put my toilet paper in my black water storage tank.

You'd be amazed at how much room toilet paper takes up!

A family of four in a 38 foot Class A motorhome with a 50-gallon tank might not make it an entire week before needing to dump. Especially if they aren't careful about what they flush down the toilet (and how much they flush).

So as you can see, it depends on your situation.

If you are dry camping, your grey water tank will also determine when you need to go dump.

It may fill faster than your RV black holding tank.

Family sitting in chairs in front of Class C motorhome

What Should I Put In My RV Black Tank?

There are only three things you should put into your RV black tank:

  1. Your excrement (human solid waste)
  2. An odor treatment
  3. Septic-approved toilet paper

THAT IS ALL. Don't put anything else down the toilet, such as tampons, diapers, or facial wipes.

These things can and will clog your black water tank if you allow them to be flushed.

The pipes used in your RV might be curvy, and they might be narrow. The less solid matter you put into them, the better your chance of NOT having a clog.

Can I Leave The Black Tank Valve Open?

NO. Do NOT leave your black tank valve open when connected to sewer at a campsite.

Doing so will allow the liquids to drain out while the solid waste from your human waste begins to pile up.

This lovely event is called a 'poop pyramid.'

pointing at black tank valve handle

Keep this valve shut unless you're actively dumping!

Gross, huh?

But as you can imagine, letting the liquids drain easily by leaving the black water tank valve open causes the solids to stay right where they drop.

Human waste (solids) needs to have a good deal of accumulated liquid to 'flush' it out of the black tank. If you let the liquid drain out as soon as you make a 'contribution', there will be no liquids left to 'move' the solids out of the tank.

You will soon learn not to do this the first time you accumulate a poo pyramid with the resulting clog.

Why Does My Black Tank Monitor Show Full When I Know It's Empty?

If your black water tank sensor constantly reads 'full', even when it's empty, there is likely something caught on your sensor.

MOST people think toilet paper is the culprit. And indeed, sometimes it is.

However, what most people don't know about is that in sewer systems, ALL sewer systems, grows what's called a Struvite.

Struvites are mineral deposits that form in the pipes and on the walls.

It's hard, and if it covers a sensor, it will read full. And there's no getting it off for the most part, without paying for someone to deep clean your tank using chemicals and high water water.

TankTech RX holding tank treatment

That said if you start with a brand-new black water tank and new sensors, using Tank Tech RX religiously can keep struvites at bay.

It's the only product that inhibits the growth of this pesky buildup.

Don't fall for the 'ice cubes in the black water tank' trick to fix your sensor issue. The Fit RV debunked the effectiveness of this theory in this video:

How Can I Fix My Black Water Tank Sensor?

As an RV owner, you may find yourself having to fix your black tank sensor so that it reads correctly. The sensor probes get debris and buildup on them, causing the tank level to read incorrectly.

The easiest way to fix a black tank sensor that isn't working is to use a liquid sensor cleaner. Remember that this isn't a guaranteed solution, and even after cleaning, your black tank level will probably start reading incorrectly again sooner than later. Which means you will need to clean the sensors again.

Learn more about how to clean RV black water tank sensors.

Tank monitor panel

Liquid RV Tank Sensor Cleaner

The easiest way to clean sensors that aren't reading correctly is to use the Unique Sensor Cleaner product. This is one of the only ways you can clean black tank sensors at home.

As the self-proclaimed most potent sensor cleaner available, Unique's Sensor Cleaner uses probiotic bacteria and enzymes to remove any buildup that is causing sensors to read incorrectly.

Follow the directions on the bottle for best results. Retreatment may be required if the first treatment doesn't solve the issue.

Unique sensor cleaner

Should I Leave Water In My RV Black Tank When I Store It?

You should leave water in your RV black tank whenever you are going to be storing it for more than a couple of weeks.

Why? Because if you leave the tank dry, especially in an arid environment, the drain seals can dry out and crack, causing future leaks.

This is especially true for the ball valve in the toilet.

Store your RV with some water in the tank and with the bowl full of water. Otherwise, you may come back to a drippy, leaky, and smelly toilet!

Can I Put Baking Soda In The RV Black Tank?

Sure, you can put baking soda in your RV black tank, but what is the reasoning for it?

Despite what you may have read, there is no reason 95% of the time to use any treatment or chemicals in your black tank.

There should be no odors coming from it if it's working correctly, aside from a brief stink when a flush happens with the overhead fan on. (If it is really hot out, then you may smell odors.)

Adding baking soda isn't going to sterilize or clean your tank.

Odors? Nope. Baking soda will not help.

Do I Need To Use Treatment Products For Tank Maintenance?

No, you don't need to use any tank treatment products in your black holding tank. Most full-time RVers don't use them.

Do a Google search in forums, and you'll see how many say they don't use nor do they need chemicals in their tank.

Save your money and spare the environment from unnecessary RV toilet chemicals.

There is one exception to not needing tank treatments. SOME RVs may have a bit of odor. Usually more in extreme heat environments.

In such a case, we would advise using a tank treatment for odors, such as Happy Camper RV treatment.

Happy Camper toilet treatment

Alternately, in colder temps, it's not even warm enough for the bacteria and enzymes in treatments to flourish and do their job.

Otherwise, there is no need to have a 'treatment' made to break anything down. Use enough water, and your system should work as designed.

The actual 'processing' of solid waste will happen in the sewer or septic system that you dump your tanks into.

What If My Poo Clogs The Pipe Leading To The Black Water Tank?

Maybe your poo is unusually hard. If so, you might find that your poo clogs your pipe leading into the tank itself.

If this is the case, funny enough, you can get yourself (yes, this exists as a product!) a poop knife.

Yep, slice your poo, and it should have no problem getting down the pipe and into the black tank! Gross? Yes.

Necessary? If it is, then it is!

What Is Clogging My Black Water Tank?

If you keep getting clogs, and you're already using a poo knife if you thought poo was the culprit, then it's likely that toilet paper is the issue.

90 degree end of sewer hose going into dump receptacle

It's not draining??? Oh no, no, no, no, no, noooo!!!!!!

You can do two things to remedy this:

  1. DON'T PUT YOUR TP DOWN THE TOILET! It sounds gross, but it's SO totally not. Put a small waste can in your bathroom and put all TP into the trash. This also saves tank space if you are dry camping.
  2. Tear up your toilet paper before using it. You can likely get by using non-septic-safe TP if you do this hack. Just tear up the TP you are about to use. Then it's much less likely to cause a clog.

How Do I Stop My Black Tank From Smelling?

Simply put, to stop your black tank from smelling, use an odor treatment product.

That said, most RV black water holding tanks don't emit any odors. For whatever reason, SOME do at times.

In hotter weather, you might smell something. Use an odor treatment in your RV black water holding tank and it should help.

Full RV park with trees and gravel road

Can I Put Bleach In My Black Water Tank?

No, you should not put bleach into your black water tank. You want to disinfect it?

Why? It's not like your camper black tank is a sanitary place at any time, full or empty.

Bleach does two harmful things:

  1. Kills off naturally occurring bacteria that can help do a little breaking down of solids in your tank.
  2. It might also prematurely break down any seals that are made to stop leaks and odors from 'getting out.'

There's no good that bleach can do for black water RV tanks.

What Brands Of Toilet Paper Are Safe For An RV Black Tank?

Any brand of toilet paper that has 'septic safe' labeled on it is safe to use in your RV black water holding tank.

If you don't care for any septic safe products, you can try using regular TP and tear it into a few pieces before use.

Toilet paper roll on top of RV toilet

So Is Costco Kirkland Brand Toilet Paper RV Safe?

Yes, Costco Kirkland brand toilet paper is RV safe because it says' septic safe' on the package.

Any TP that says 'septic safe' is safe for RVing use in your RV blackwater tank.

What's The Best Way To Guarantee I Never Have A Black Water Tank Clog?

The best way to avoid RV black water tank clogs is NOT to put any toilet paper down the toilet!

TP is the number one cause of clogs in an RV. Putting used toilet paper in the trash sounds gross, but it's 0% gross in reality.

Some people use an open trash can, some use one with a lid, and others use a diaper genie, which is overkill if you ask us.

Waste basket full of used toilet paper

Kelly's actual TP trash can. See? No brown. Easy peasy.

The only smell you're going to smell is the same amount of smell you have under any circumstances.

You're going to smell your bowel movement as it's coming out. That's it!

Used TP in the garbage does NOT have a lingering smell. As a bonus, this practice also saves tank space when you're dry camping in your RV.

If your black wastewater is your limiting stay factor, you may be able to extend your stay by two or three days by putting your toilet paper in the trash instead of into your camper black water tank.

What's The Difference Between A Gray Water Tank and A Black Water Tank?

An RV usually has two wastewater holding tanks.

The black water tank holds sewage, while the gray water tank holds everything that goes down all RV drains.

Very small RVs may have only one wastewater tank. These collect gray water as well as everything that goes down the toilet.

Black & gray tank valve handles

How Do I Perform A Tank Flush?

To do a black tank flush, first be connected to a dump station using an RV waste hose.

Then connect a water hose to your flushing apparatus (Sometimes found as one of the top RV accessories you must purchase).

If your RV comes with a flushing system, all you need to do is connect the hose to the flush input.

Let the water rinse for a couple of minutes, while the black tank valve is open. Best to have a clear connector to be able to see when it has come totally clean.

Conclusion

An RV black water tank collects everything that goes down the sewer line (toilet).

It stores the waste water (human waste) and toilet paper until full. Once full, the waste tanks should be emptied with a sewer hose.

Toilet brush usage instructions illustration

RV toilets work a bit differently from house ones. You must use enough water so you don't get a clog, use appropriate TP or don't put it down the drain, and dump when needed.

It's easy to do if you are on a camping trip and have sewer hookups at your campground.

Simply connect your sewer hose to your sewer connection at the campsite, and dump when needed.

Otherwise, you'll need to find a dump station on your own.

There's very little maintenance to do on these tanks.

Just know that they can and will clog if you don't follow some very basic rules about using the toilets in these recreational vehicles.

That's it! Now get out there and enjoy your RV.

Kelly Headshot

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. 

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