How to Dump Your RV Black/Gray Tanks: It's Time to Talk About Poop on the Internet

Raise your hand if you're super excited to dump your RV waste tanks.

Yeah, I didn't think so.

It's the part of RVing everyone dreads at first, and it's one task you don't want to mess up if you can help it. But trust me—eventually, it'll become such a mundane part of RV life you won't think twice about it. I'll show you the right way to dump your waste tanks and avoid messy mishaps (though they do make good stories to share at the RV park). Stick with me, kid, and I'll even tell you about the time my friend accidentally filled his gloves with poop water.

Bet you didn't think when you woke up today that you'd be talking about poo with a chick on the internet, did you? Alright friends, let's roll up our sleeves and (not) get our hands dirty.

In this article:

When to Dump Your Black and Gray RV Water Tanks
How to Dump Your Black and Gray RV Water Tanks
Should You Leave Your Black/Gray Valves Open?
How to Use an RV Black Water Flush
Where to Dump Black and Gray Water

Watch now: How to Dump Your RV Black and Gray Tanks

Quick review: Your black water tank is where all your toilet waste goes. Your gray water tank is where your sink and shower water goes. Your freshwater tank is where your drinkable (potable) water is stored before it eventually gets used and flows into your waste tanks. Read more about how your RV water system works here.

When to Dump Your Black and Gray RV Water Tanks

The general consensus is to dump your black tank when it's about 2/3 of the way full. (As a point of reference, this usually takes around 3 - 5 days on average.) This will ensure there is enough water to suspend any solid matter and allow the tank to drain. If you have to dump before this point, fill the tank with water first. Your gray tank is less finicky—you can dump when it's about 2/3 full as well, or you can leave the gray valve open at the sewer connection so the waste water consistently drains rather than filling up (more on that below).

How do you know when your tanks are full? Most RVs come with sensors to let you know how full your tanks are. That said, sensors are notorious for getting gunked up (especially black tank sensors) and providing false readings. That's why it's important to routinely clean your tank with a tank rinser. Alternatively, you can use a sensor system designed to prevent buildup, like Miracle Probe Sensors, or one that installs on the outside of your tank, like the SeeLeveL Tank Monitoring System / senders.

Of course, you should always empty your tanks at the end of your camping trip, regardless of how long it's been since the last time you dumped. You don't want waste water sitting for weeks or months in your RV. If your tanks are low, fill them with water and then dump. You can fill your tanks by turning on the sink or shower for gray tanks and by either flushing the toilet or using a back flush for black tanks.

RV Tank Sensor Panel - Black Tank 2/3 Full

Pictured: a tank monitor in an RV. The bottom image shows that our black tank is 2/3 of the way full.

Jake H. says

"About a year ago...I was wearing gloves while I was dumping my tanks. I didn't have this 90 [degree fitting], and I didn't have a vapor lock. So I just had the end of my hose sticking in the sewer pipe. Well...I was holding the lid open and I went to check it, and I pulled it up, and my glove filled with "material water." And since that day, I just have gone with the method of when I'm dumping my tanks that's all I'm doing, and when I'm finished dumping them, I just wash my hands.... You don't wear gloves when you go to the bathroom. You just wash your hands afterward."

Amber S. says YES

"I might have a different position if I a) owned rather than rented RVs or b) had Jake's experience with poop gloves. But personally, I always wear gloves when dumping tanks. If you rent RVs, the owners often leave a pair of hardy gloves in the storage compartment for you. But I prefer buying them at the dollar store for a buck and throwing them away afterward, so I know I'm not sticking my hand into any bacteria-ridden gloves. Although I'm generally okay getting my hands dirty when camping, I'm not messing around with waste hoses and dump stations without a barrier. Poop gloves sound like the stuff of nightmares (sorry, Jake), but to me that's all the more reason to use a clear fitting when you dump and be careful with what you're doing."

How to Dump Your Black and Gray RV Water Tanks

You always want to dump your black water tank first. This is because you'll use the gray water to wash out the inside of the hose afterward to make sure no toilet gunk lingers behind. I'll list out all the steps first in case you want to copy/paste them into your phone or print them out for easy reference at the campsite, then I'll go into more detail below.

The short & sweet version:

Make sure your tank valves are closed and remove the sewer cap
Secure one end of your sewer hose to your black tank valve and the other end to the sewer hookup
Open your black tank valve, wait for the tank to drain, then close the black valve
Open the gray valve, wait for the tank to drain, then close the gray valve
Use a flush valve to rinse out your tanks (optional but recommended)

The detailed version:

Step 1: Make sure tank valves are closed; remove sewer cap

This step is pretty straightforward. Always make sure those valves are closed before taking off the sewer cap! You don't want anything flowing out before you're good and ready. You wouldn't be the first RVer to forget to close their valve, but this is a mistake you'll probably only make once.

Step 2: Secure hose to waste valve and sewer hookup

Typically, you just place your hose over the RV waste valve and twist the lock into place. Give it a little jostling to make sure it's secure—that water can come out with some force behind it, so you don't want the hose disconnecting at the worst moment.

Next, attach your hose to the sewer connection. Use the sewer lid or any nearby rock/brick to help secure the hose in place, if needed. Again, make sure it's secure so the force of the water doesn't push it back out.

Step 3: Open black tank valve, let tank drain, close valve

Time to let it flow—open that black tank valve! If you're not sure which one is the black valve and which is the gray, check for some sort of indicator on your RV itself (for instance, your gray water handle might be gray or be labeled as such). If not, you can check your owner's manual, or else get down and check out the pipes these handles are connected to. The wider one will be the black tank pipe, since the gray pipe theoretically only carries water and the black pipe carries...other stuff.

Let the tank drain until it's empty, then shut the black tank valve.

You can just see the narrower gray pipe and the wider black pipe. Both sewer pipes end up flowing out the same valve, but they run from different locations under your RV.

Pro tip: If you only buy one upgrade for your RV, make it a clear sewer fitting. You can get one that attaches to either the trailer end or the sewer-connection end of the hose (although they're so inexpensive you're even better off getting both). You may not want to see what's going on inside the hose, but it's extremely helpful to know when the tank is finished draining rather than trying to listen for flowing water. The last thing you want to do is disconnect prematurely. That's how you get poop water in places you don't want poop water to be—like in your gloves.

Step 4: Open gray tank valve, let tank drain, close valve

Pull your gray valve next. Again, let the tank drain completely just like you did with the black tank. Then close the valve.

Step 5: Rinse tanks

Your tanks are mostly clean now, but we want to take it a step further and really make sure nothing is sticking to the insides. We'll do this by rinsing your tank with a built-in or added black tank flush or tank rinser.

Not sure how to use a black tank flush or tank rinser? We'll show you how in the section below.

Should You Leave Your Black/Gray Valves Open?

THE GRAY VALVE

Some RVers prefer to leave their sewer hoses hooked up to the sewer connection with their gray valve open so that the waste water just flows right into the sewer hookup.

This is a matter of personal preference and has a lot to do with dumping frequency. if you're camping with a large family, you might have to dump more often and prefer to leave everything hooked up to save time. You might also not want to worry about your gray tank filling up unexpectedly (such as when you're about to take a shower), so you might want to leave the valve open to continuously drain. Just close it up and add some water via the sink or shower when you get ready to dump the black tank so that you have some gray water to flush out the sewer hose with afterward.

Personally, though, I'm a fan of leaving the gray valve closed when I'm not dumping. Why? Your tanks work best when solids are suspended in (and eventually flushed out by) the liquids. You really shouldn't have solids in your gray tank (just sink and shower water), but the reality is that food particles have been known to sneak down there and stick to gray tank walls. In addition, gnats and flies have been known to make their way up inside open valves and into your RV. I love nature as much as the next camper, but personally I prefer the bugs sleep outside.

RV hose connected to waste valve and dump station

THE BLACK VALVE

Leaving your black valve open is a huge no-no in the world of RVing. This is because it's a surefire way to start building your very own Poop Pyramid.

What on earth is a Poop Pyramid, you ask?

A Poop Pyramid is a dreaded thing that forms when biomaterial (a fancy way of saying poop) collects at the bottom of the tank, and builds. And builds. Eventually it builds so much that your tank holds one giant pyramid worthy of ancient Egypt. A sufficient amount of liquid in your tank helps keep these solids moving rather than sticking to the sides of the tank. So do yourself a favor and never, ever leave your black tank valve open, or you may end up like the poor souls unclogging their black tanks after the worst has already happened.

How to Use an RV Black Water Flush

No discussion of dumping RV tanks would be complete without mention of the black water tank flush. Basically, these tank rinsers blast clean water into your empty tank and power-wash out any remaining residue (this is often referred to as "flushing" or "back flushing." A lot of RVers prefer to do this every time they dump. This isn't required, but it is a pretty easy chore that helps prevent odors and keeps sensors working properly. So all in all, unless you're in a hurry, I'd recommend finishing your dumping routine with a good tank flushing.

There are different kinds of black water flushes, but they all work more or less the same way:

Connect a flush hose to your tank and the city water connection. (DON'T use your fresh water hose as a flush hose—if something goes wrong and there's backflow, you don't want that waste water in your drinking hose.)Hopefully your black tank flush will be labeled as such if you have one. If you know you've got a black tank flush but aren't sure where it is on your RV, check your owner's manual. If you don't have a built-in black flush, you can install a permanent tank flush yourself. Alternatively, you can use a flush valve that connects to your sewer hose. (The Flush King is a popular example of this.) Lastly, you can use a tank rinser that you can stick down the toilet. You can also use one of these in conjunction with one of the above flushes for extra gunk-blasting power. My buddy Jake (the poop glove guy mentioned above) has a flush valve that does a pretty decent job keeping his black tank clean, but we once used a Swivel Stik down his toilet, and it managed to dislodge some stuff the flush valve missed.
Built-in Black Tank Flush on RV
Flush Valve with Flush Hose Connected
Swivel Stik Tank Rinser
Make sure your black tank valve is OPEN. Then turn the water on.
Keep the water running until everything starts to flow out clear. Then you can shut the water off and close your black tank valve again.

Where to Dump Black and Gray Water

A designated dump station/sewer hookup is always a safe bet. But what if you don't have one available? Can you dump gray water on the ground? Can you dump your black tank into your home septic system? (Answer for both: maybe, with some stipulations.)

Below, we've addressed some of the most common dump location questions. (Basically, the overall answer amounts to this: check any local or state laws, use common sense, and be considerate to others.)

Where to Dump RV Black and Gray Water Tanks

So—are you super excited to dump your waste tanks yet? Hopefully with these tips, it'll be the highlight of your trip! Okay, maybe not, but hopefully the above advice has a) helped calm your first-time dumping nerves and b) helped prevent any mishaps. If you do have any such stories (or if you have more questions about how to avoid them), let us know in the comments below!

As a content writer for etrailer, I might spend my morning loading and unloading a bike on five different bike racks to figure out which is easiest to use. I might be in the parking lot, taking pictures of an impressive RV battery setup our techs came across in the shop and discussing the benefits of the setup with the owner. I might spend an afternoon in a manufacturer training classes for some hands-on experience with new products, and then sit down to assemble all this information into a coherent article.

At etrailer, one of our core values is that we are always learning, and I learn something new every day. I start each morning with the goal in mind of taking all of this information and figuring out the best way to answer the questions people ask us (and the ones they don’t know to ask yet), and helping people get the solutions they need to make their lives easier, safer, and more fun. I’m a DIYer at heart, so it brings me great joy to help a fellow DIYer find what they’re looking for, whether that’s a product, an answer, or a community.

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Written by: Amber S.

Updated on: 10/9/21

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