5 Reasons your RV has Two Grey Water Tanks

RVs are more popular than they’ve ever been, both for weekend warriors and long-term living. Because of the growing need for RVs that you can use long-term and for large families, designers are getting creative with how to maximize water tank capacity. While some designers simply install larger grey tanks, others design their RVs with two grey water tanks. 

Typically, RVs have two grey water tanks because it allows people to boondock longer without having to dump their tanks. There are usually space restrictions to the underside of an RV, which doesn’t allow for one massive tank, which means you need two smaller ones in different frame locations.  

While it can be slightly inconvenient at times, there’s no denying that multiple grey water tanks are a blessing. In this article, we’ll look at more reasons why RV designers do this and answer more of your RV water tank-related questions. 

Why Do RVs Have Two Grey Water Tanks? 

It’s becoming increasingly common for RVs to have two grey water tanks in place of one large one. In fact, there’s a good chance if you have a newer RV, that it has two grey water tanks, and you don’t even know it. Here are some of the main reasons that camper designers do this and the benefits it adds. 

More Storage Capacity 

The main reason that RVs have two grey water tanks instead of one is for more storage capacity. If an RV only has one grey water tank, it can average in size from 40 gallons to 90 gallons depending on the size of the RV. When they have two grey water tanks, however, they average in size from 25 gallons to 55 gallons, depending on the size of the RV. 

This extra grey water capacity makes it possible to boondock or camp off-grid for longer without having to dump your tanks. 

Small Tanks are Easier to Maintain 

As a general rule, the smaller the storage tanks are, the easier they are to maintain. Large, 90-gallon tanks are all but impossible to maintain and keep smelling good for long. However, when you have two smaller tanks, maintenance might take a tad longer, but it’s more effective. You’ll keep your grey water tanks cleaner and smelling better when they’re smaller. 

Size Restrictions 

Another big reason that RVs have two small water tanks instead of one large one is because of size restrictions. RVs have to cram a lot of pipes, metalwork, and other components underneath your camper. In most cases, there simply isn’t space for a single, massive storage tank. Instead, it’s easier to fit two smaller tanks under the RV because it interferes with fewer other components. 

Washing Machine Hookup 

Most newer campers come with the option of adding a washer and dryer. If your camper has this option, the washing machine usually has a dedicated grey water tank. 


If you have two bathrooms or a kitchen that’s spaced far apart, it’s common to have two grey tanks and sometimes two black ones. Rather than having plumbing pipes run all around your RV, builders prefer to have individual tanks with a single drainage pipe connected to the drain valve. 

How Do You Empty Both Grey Water Tanks? 

The nice thing about multiple grey water tanks is that they add more storage capacity without adding more work. In most cases, the tanks are connected with a pipe and valve, which means they’re easy to empty. Here are the steps you need to follow to empty your grey water tanks, as well as any other tanks on your RV. 

  1. Connect your sewer hose to the outlet port on the bottom and side of your RV. 
  2. Connect the other end of the hose to the dump station or sewage connection at your campground. 
  3. Open the grey water valve to initiate the flow of grey tank 1. 
  4. Wait until water stops flowing out of the sewer hose and close the grey tank valve. 
  5. Repeat the process with grey tank valve 2. 
  6. If the grey tanks are connected, you only have to perform this step one time, and both tanks will empty. 

How Do You Connect Two Grey Water Tanks to Dump at the Same Time? 

In cases where the two grey tanks aren’t connected on your RV, you may want to connect them. To do so, you’ll have to crawl underneath your RV and remove the protective cover concealing the underbelly. Most campers will have a valve allowing you to alter the flow of grey water, and you can connect the tanks by opening it. 

However, if your RV doesn’t have this valve, you’ll have to reconstruct your plumbing system to connect the two tanks. You’ll have to run a sewer pipe from one tank to the other and install a waste valve in case you ever want to close it. 

Connecting your grey tanks isn’t required and might be more work than it’s worth because there’s really no upside to it. It means you have to open one less valve when you’re draining your tanks, but that’s about it. 

Another option instead of connecting them together would be to purchase a wye adapter so both tanks can be hooked up to your sewer connection at once.

Here are two products that will solve your problem about connecting both of your tanks to one sewer connection:

Frequently Asked Questions 

Does RV shower water go into the grey or the black tank? 

RV shower water goes to the grey tank on your RV. The black tank is reserved for water and waste from your toilet. 

Does the grey tank drain into the black tank? 

Your RV’s grey water tank and black water tank are two separate entities and aren’t connected to one another. However, they will drain out of the same sewer hose and exit port on your RV. 

Is it ok to leave RV grey water tank open? 

Because of convenience, many RVers leave the grey water tank permanently open on their RV. However, there’s a chance that sewer smells will creep up the pipes and emanate throughout your RV. There’s also a chance that insects and small animals can crawl up the sewer and into your RV. 

Do RV’s have two Black water tanks?

Yes, some RV’s have two black water tanks as well. Here’s why.

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