RV Water Tanks Basics

Chelsea Gonzales
Published on February 16th, 2021

The RV life is fantastic to be sure. That said, it isn’t all as glamorous as it might seem. Among the least glamorous aspects of RV living are the water holding tanks. In fact, we’d even go so far as to say that dealing with the contents of RV water tanks is probably the least fun part of any RV adventure. 

That said, in order to go on fantastic RV adventures, we must learn to use these tanks efficiently. So learn we do. 

Now, if you’re new to the RV world, you might be wondering what on earth we’re talking about. If that’s the case, you’ve come to the right place. Here we will discuss the ins and outs of RV water tanks so you can head into your first RV trip knowing everything you need to know about using and maintaining them. 

Let’s begin. 

Dripping faucet

What are RV Water Tanks?

The first question many people have is simply: what are RV water tanks? This is a valid question. After all, if you’ve never been RVing, you really don’t have any reason to know they even have tanks. 

As you might have guessed, RV water tanks are made to hold water. They are attached to the underbelly of your RV and are connected to the RV plumbing so that they provide the fresh water that comes out of your taps when using the RV pump, and catch the wastewater that goes down the drains in your motorhome or travel trailer.

This gives you the option to camp without any hookups, as you have fresh water on board and a way to hold onto your dirty water until you find a suitable place to dump it. 

Types of RV Water Tanks

There are three different types of RV water tanks. These include:

  • Freshwater tank — Used to hold clean, potable water for showering, washing dishes, cooking, etc. 
  • Gray water tank — Used to hold used water that goes down the sink and bathtub/shower drains. 
  • Black water tank — Used to hold the waste that goes down the toilet drain. 

Each of these must be cleaned and maintained. If taken care of properly, an RV water tank can last years or even decades. 

How to Fill an RV Freshwater Tank

In order to use your freshwater tank, you will first need to fill it. To do this, ensure the fresh water drain valve is closed. Next, locate the fill-up on the side of your trailer or motorhome. This is usually labeled as “freshwater fill-up” or “city water”, making it easy to find. Remove the cap on the fill-up and place a clean freshwater hose inside. The other end of this hose should be attached to a potable water source—ideally along with an in-line filter, although that’s optional—which will then be turned on and left to run until the tank is full. 

You can watch the tank level indicators on the control panel in your RV to get an idea of when the tank is almost full. If water begins backing up out of the fill-up spot before the level indicates the tank is full, turn off the water, remove the hose, allow the existing water to drain down into the tank, and then resume filling. (In those instances, you may get a bit of back-spray once the water’s turned off, so anyone standing near the fill-up should be aware of that.)

Note that non-potable water should never be used to fill a freshwater tank. If you accidentally fill your fresh tank with non-potable water, be sure to clean it thoroughly using the directions further below before using it again. 

How to Dump an RV Wastewater Tank

The fresh water that you use will become wastewater, which will in turn make its way into the gray and black water tanks. Obviously, you can’t carry your used water with you everywhere, and the tanks only have so much capacity besides. Therefore, you will need to dump these tanks now and again.

If there isn’t a sewer hookup at your campsite or a dump station in your campground, you will need to locate a dump station elsewhere. We recommend using Sanidumps or RV Dumps to do this, but calling around to area campgrounds and truck stops could also work. 

Once you arrive at your dump station of choice, the process is as follows:

  • Put on disposable gloves. 
  • Pull the RV up so the dump pipe (typically found at the lower back on the driver’s side of your rig) is lined up with the sewer drain.
  • Remove the caps from both the dump pipe and the sewer drain. 
  • Connect one end of a sewer hose to the dump pipe and use the adapter to screw the other end into the sewer drain in the ground. If there are no threads for the adapter to connect to, you’ll need some other way of holding the hose end in place, whether it’s heavy planks of wood, a large rock or two, or a companion holding it with their foot.
  • Once both ends of the hose are secure, pull the valve to dump the black tank first. 
  • Listen and feel for the tank to finish dumping. It may take a while.
  • When no more water is draining from the black tank, close the black tank valve (never forget this step) and open the gray tank second.
  • Listen and feel for this tank to finish dumping. 
  • When both tanks are empty, ensure both valves are fully closed and detach the RV end of the sewer hose. 
  • Use a non-potable water hose—meaning, something other than what you use for your fresh water—to spray water into the hose, ensuring it is rinsed well. You may want to give the hose a bit of a shake afterward to get all the drips out before the next step.
  • Detach the hose from the ground (making sure to get your adapter) and place the hose and adapter into an appropriate storage location. 
  • Rinse any wastewater that may have made its way onto the ground down the drain and replace the caps on the dump pipe and the sewer drain. 
  • Remove gloves and wash hands and arms thoroughly. 

Cleaning Your Freshwater Tank

Occasionally, you will want to clean your freshwater tank. We recommend doing this at least once a year, but many people choose to clean it more often, especially if questionable water sources have been used or if they’ve allowed others to use their rig. 

To clean a freshwater tank:

  • Drain the system — To do this, turn off the water heater and let it cool completely. Next, find the low point drain on your RV and open it, allowing all water to drain out. Close all drains. 
  • Add the bleach water — You’ll need ¼ cup of bleach for every 16 gallons of water your freshwater tank holds. Add this bleach to at least a gallon of water and use a funnel to pour it into your freshwater tank. Fill the freshwater tank the rest of the way with potable water. 
  • Run it through the system — Run the bleach water mixture through the entire system by turning on your water pump and opening all of the faucets. Leave them on for about 2 minutes. 
  • Let it sit — Top off your freshwater tank with potable water once again and then let the bleach mixture sit in the tank overnight. 
  • Drain and flush — The next day, drain your fresh water tank using the aforementioned drain valve. Close the valve, fill the tank with potable water and run the clean water through the system by turning on the pump and opening all taps. 
  • Repeat — Repeat the last step until the bleach smell is completely gone.
  • Replace and refill — Once the bleach smell is gone, replace any water filters the bleach water went through and refill your water heater tank.
Dumping RV tanks
Image source: Mandruss

Cleaning Your Wastewater Tanks

Wastewater tanks get gross fast. For this reason, we recommend cleaning them much more often. In fact, black water tanks should be cleaned every single time you dump, and some choose to do the same for their gray water tanks. 

Fortunately, cleaning wastewater tanks isn’t hard at all. To do this, follow the steps below:

  • Dump the tanks using the instructions above. 
  • Use a flush valve to remove any build up on the tank walls.
  • Add water to cover the bottom of the tank (about 4-5 toilet bowls full).
  • Add a tank treatment such as TST RV Tank Cleaner

Following these steps after dumping will help you avoid stinky smells as well as clogs. 

Other Things to Know About RV Water Tanks

Now you know all of the basic things you need to know about RV water tanks. That said, the things mentioned above are far from the only things to know about these tanks. 

Below are a few more important things to know about your RV wastewater and freshwater tanks. 

Bigger is Better

If you plan on boondocking at all, the bigger your tanks are, the better off you’re going to be. A bigger freshwater tank means more clean water for use during your off-grid camping trips. Meanwhile, bigger waste tanks mean you have a place to put used water. 

All that said, it is important to consider the fact that water is very heavy. A full 40-gallon tank of water weighs about 332 lbs. Carrying this amount of water can seriously reduce the amount of cargo you’re able to carry, so pack wisely. 

Never Dump on the Ground

The number one rule of RV wastewater tanks is that you never dump on the ground. This is especially true when it comes to black water, but dumping gray water is frowned upon as well. Take the time to take your wastewater to a dump station. Your RV neighbors will thank you for it. 

Consider What You Put Down the Drain

Because wastewater isn’t immediately swept into the sewer in an RV, things that get washed down the drain have a tendency to settle in the bottom of the tank or get stuck to the tank walls. This can cause bad smells and clogs. Additionally, certain chemicals could cause tank damage. 

Therefore, you will want to carefully consider what you put down the drain, and flush toilet paper with plenty of water. 

Careful in the Cold

Finally, it is important to note that RV water tanks can freeze. If this happens, the tank may crack, rendering it useless, especially if the crack is too big to repair. 

For this reason, we highly recommend investing in and installing tank heaters to keep your RV tanks warm during the colder months. 

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