What Is a Black Water Tank? All You Need to Know About This RV Essential

Black water is wastewater. When you flush the toilet, that’s black water.

So, what is a black water tank? Simply put, a black water tank is a wastewater tank that holds black water until you’re ready to dump it.

Your black water tank is the unsung hero and is why you don’t have to empty a nasty RV toilet into a pit at the campground. You don’t have to worry about carrying as much water in your RV, either—especially when boondocking. But it’s easy to ignore black water tanks until something goes wrong.

But first, to avoid confusion and help you avoid any “uh-oh” moments, let’s define the difference between a black-water tank and a gray-water tank.

What Is a Black Water Tank?

The first thing to understand about black water tanks is that they’re an absolute lifesaver.

These big, heavy tanks hold all the wastewater from your toilet. This waste can contain pathogens, like viruses and bacteria, so RV owners must manage it carefully.

The black water tank is on the bottom of your rig and has a larger capacity than your gray water tank. It’s pretty large compared to anything else in your rig. In fact, it requires regular emptying to ensure proper functioning.

Black water tanks are a bit more complicated than you might think. They require careful and regular emptying to ensure proper functioning.

Though the smell of a black water tank can be too much for some, RV owners must make a point of cleaning, maintaining, and emptying this tank.

And, let’s admit it: the tank will emit some foul smells. It’s just the way nature works, and there’s nothing you can do about it.

What Is a Gray Water Tank?

 It’s common for an RV to have a gray tank.

A gray water tank holds wastewater from your sinks, showers, or other fixtures in your RV. Eventually, depending on your RV system, this water may drain into the black tank.

This system allows you to maintain the quality of your drinking water without having to dispose of the wastewater. Most campgrounds now prohibit untreated gray water from entering their sewer systems.

This is why a gray water tank is so important when staying at a campground that does not have sewer hookups.

What Are Portable RV Black Water Tanks?

If you enjoy going on RV trips, you probably know that one of the most important things to pack is a portable RV black water tank. This simple device is an excellent way to ensure your RV stays clean and fresh while you’re away from home.

By using a portable RV black water tank, you can transport the contents of your black and grey water tanks to a dump station so you can properly dispose of them.

RV portable waste tanks have a handle and wheels, allowing you to easily pull them across dumping stations and campgrounds.

When using a portable RV black water tank, take as much care cleaning and flushing it as when you empty your regular RV black tank.

How Do You Clean Your RV Black Water Tank?

So, what is a black water tank, and how do you clean it? RV black water tank cleaning is pretty simple nowadays. Plenty of great commercial products are available that help you maintain your tank regularly and avoid the embarrassment (and headaches) from a dirty tank, built-in odor, and even an overflowing system.

But how do you actually do that?

When you begin your trip, add RV black water tank treatments to your black tank. These treatments are commercially available in packet or liquid form. Be sure to add about a gallon of water, which helps the chemicals clean better.

Let it sit overnight once you’ve added the water and chemical treatment to your black water tank. Then comes the dreaded part—cleaning and draining. This is where things get messy, but don’t worry; the process isn’t that complicated.

This guide will walk you through how to deep clean your black water tank in between trips:

  • Make sure you use the right chemicals (like Pine-sol or laundry soap) when cleaning your black water tank. You’ll want the kind that breaks down the solid waste and toilet paper so that it doesn’t clog up your pipes during dumping.
  • Drain the black water tank completely, then fill it 3/4 full with clean water and your cleaning chemical of choice.
  • Drain the tank again.
  • Fill it up again to 3/4 capacity with clean water.
  • Repeat this last step until the water runs clear.
  • Every time you dump or fill your tank, use some of the same chemicals to keep smells at bay.

How to Dump Your RV Black Water Tank

Dumping waste from RV black water tanks is not a task everyone likes.

If you’re new to RVing, here are a few tips to ensure you don’t accidentally break the law or hurt yourself.

Traveling alone on your RV adventure? You may dump your black water tank after a week or, at most, 10 days.

On the other hand, if you’re camping with a big family (or traveling in an RV with a small tank), you may need to empty the tank every 1 to 2 days.

If you’re only going to be away from home for a few days, it’s probably not worth the effort of driving somewhere special to dump—although there are exceptions if your rig has small tanks that fill up quickly or if there aren’t any dumping stations within a reasonable distance.

Dumping your RV’s black water tank is not as hard as you think.

Follow these steps, and you’ll be all set to go!

  1. First, put on a pair of protective rubber gloves. You don’t want to get that stuff on your hands!
  2. Connect one end of the sewage drain hose to the RV black tank valve.
  3. Secure the opposite end of the hose to the valve at the dumping station/sewer line.
  4. Empty the black tank.
  5. Do this by pulling the valve, remembering to allow enough time for it to drain completely and cleanly.
  6. Flush the black tank completely with water.
  7. You may use water from your gray water tank for this step.
  8. Drain the tank completely.
  9. Repeat the above two steps (flushing with the gray water tank water).
  10. Close both valves after rinsing out any residual residue inside of them.
  11. Remove both hoses from your RV water tanks and store them until next time.

How Often Do You Dump Black Water Tank Systems?

Now that we’ve answered, “What is a black water tank?” the next question is, “How often do you need to dump RV waste?”

When camping in a self-contained RV, you might notice that the sensors on your black water tank are pretty helpful—they let you know when it’s full and needs dumping.

But what about when you’re not camping?

Most self-contained RVs have a sensor that tells you how full each tanks is, including the black water tank. Dump your tank when the sensor indicates it’s near 3/4 full capacity.

However, with some smaller RVs, there’s no sensor. You’ll need to keep a careful eye on the water level to determine the fullness of the black tank.

If you’re like us, you don’t want to store wastewater in your tanks for long periods! So, here’s how often we recommend dumping your black water tank: after every single trip. Yes, even if it’s just for a day trip.

You might think that because it’s only been one day, there hasn’t been time for anything to clog up in there. But, even if nothing has happened yet, we’d rather be safe than sorry. So do yourself a favor and empty that thing when it gets full!

How Long Can You Leave Black Water in RV Holding Tanks?

When camping, you don’t want to think about your black water tank.

It seems like many people are confused about how long you can safely leave your black water tank full. We’re here to clear things up!

Most camping experts confirm that you can leave black water in the RV tank for up to ten days. Most, however, state that you should empty it after no longer than one week.

The reason is simple: bacteria and chemicals in the tank can start to break down after a while.

In fact, some of these bacteria can even begin to grow mold. This will make your RV smell bad and could even cause health problems for anyone who breathes in the fumes from the moldy and pathogen-filled wastewater.

Related: How Often Do You Need to Dump RV Waste?

FAQs: What Is a Black Water Tank

What’s the difference between black water and gray water?

Black water is water that drains from the toilet and contains human waste. It requires its own tank and careful disposal so as not to contaminate the surroundings. Gray water is wastewater that drains from your shower and kitchen and bathroom sinks. It’s usually clear but can be tinted a light brownish color. You can use gray water to water plants and clean things like floors.

How can I tell if my black tank is full without a sensor?

Your black tank is full or nearly full when the smell gets too bad to ignore. You can also tell the black tank is full by listening to the sound of the water inside. The color of the water will also change slightly when it starts becoming saturated; it’ll turn from clear or light brownish color into a darker brownish color.

Why does my black tank show as full when empty?

These sensors are associated with black and grey tanks. Sometimes, these sensors can give false readings, indicating a full or partially full tank even after completely emptying them.

Are RV black water sensors accurate?

RV black water level sensors are a great way to monitor the water levels in your RV black tank. They are far more accurate than probe sensors and give you a better idea of how much space is still available in the tank.

Final Thoughts: What Is a Black Water Tank?

What is a black water tank? We hope this blog post has comprehensively answered this question for you.

Your black water tank has a specific purpose—waste disposal—and you should treat it as such. Most of the trouble comes from leaks, but with proper precautions, you can easily prevent this.

If you have any other questions about your RV’s black water tank, or if you need assistance finding the best portable toilets for your needs, we encourage you to contact Wilkinson Portable Toilets if you’re in Placerville, CA.

Let us help you have a great time on your next camping or road trip in your RV!

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