The Ultimate Guide to RV Water Tanks

Published on February 14th, 2022

Having plumbing on the go is one of the more awesome things about RV travel. But one of the less awesome things? Dealing with the RV water tanks that make said plumbing work. 

Honestly, RV holding tanks aren’t something many people think about when buying or renting an RV. This is understandable. They are about to acquire the ability to adventure anywhere, so why would they be focused on something as trivial as tanks? However, the truth of the matter is that water tanks are a very important part of any RV, and knowing how they work and how to care for them is crucial. 

Not sure where to begin learning about your RV water tanks? You’ve come to the right place. In this guide we will cover everything you need to know about RV fresh water and wastewater tanks so you can head into your first camping adventure with complete confidence. 

RV water tank

The Different Types of RV Water Tanks

First, let’s talk about the different types of RV water tanks. These include your water tank, black water tank, and gray water tank. All three serve an important purpose, and you will want to know how to care for each while out on the road. 

Fresh Water Tank

As the name suggests, your fresh water tank is used to hold fresh water. All water put into your fresh water tank needs to be potable and should be filtered, as it is used for drinking, cooking, showering, etc. Water stored in this tank is pulled through the RV plumbing system by a pump when a tap is opened. This allows the user to have running water even when a spigot is unavailable, making dry camping a much more comfortable experience. 

These tanks can be anywhere between 15 and 100 gallons in capacity. Obviously, those who boondock often will want a larger tank, but it’s important to keep in mind that water is heavy and can quickly put you over the carrying capacity for your rig. 

Gray Water Tank

The gray water tank is what holds the water used to wash your hands, shower, or wash dishes. In most RVs, all sinks and showers drain into the gray water tank. Once in the tank, the water will sit until dumped by the user. Gray water should always be dumped at a designated sewer dump, never on the ground. 

Most gray water tanks are around 40 to 50 gallons. That said, the capacity of these tanks will vary from one RV to another, so be sure to check to see what size yours is. 

Black Water Tank

Finally, there is the black water tank. If you thought the idea of a gray water tank was gross, you’re sure to be thoroughly disgusted by the black water tank. Why? Because this is the tank that the toilet drains into.

Once the toilet water is flushed, it sits in the black water tank until the tank is dumped in an appropriate sewer dump. Obviously, black water shouldn’t be dumped on the ground either. 

As far as capacity goes, you can expect your black water tank to hold anywhere from around 15 gallons to 65 gallons or so. 

Using Fresh Water Tanks

Now that you know what each tank does, let’s discuss how they all work. We’ll start with RV fresh water tanks. As mentioned above, these are used to hold fresh, clean, potable water for drinking, showering, and washing dishes and hands. 

Filling RV Fresh Water Tanks

To fill an RV freshwater tank, you will need to find a trustworthy potable water source. We like using Campendium for this purpose. 

When you find a good source, you will pull up next to the spigot, attach a fresh water hose to the connection point and put the other end of the hose into the freshwater fill port on the side of your RV. Turn on the water and watch the tank sensors in your RV to know when the tank is full and the water should be turned off. 

If you accidentally overfill the tank, it will overflow onto the ground. This isn’t a problem, so don’t worry if it happens to you. If overflow starts to happen before the tank is full, it is likely because the water pressure is too high. In this case, turn off the water, allow the excess to drain into the tank, then turn the water back on with a bit less pressure. 

Maintaining RV Fresh Water Tanks

Maintaining your fresh water tank is as easy as ensuring you always fill with clean potable water. You’ll also want to dump the freshwater tank if it won’t be used for long periods of time in order to avoid letting water sit in the tank for months. Additionally, it’s a good idea to clean the fresh water tank at least once a year. See instructions for doing this further below. 

Bathroom sink

Using Black and Gray Water Tanks

For the most part, using black and gray water tanks is pretty straightforward. You use the water in your rig and it automatically drains into the tanks. Once your tank sensors read full, you will need to dump your tanks. 

Of course, it’s a good idea to know how to dump the tanks, as well as how to maintain them to ensure they stay usable for as long as possible. Below are our top tips. 

Dumping RV Black and Gray Water Tanks

To dump your tanks you will need to find a campsite with a sewer hookup or a dump station. For this, we like to use Campspot or Campendium. 

  • Once you’ve located a dump spot, pull up next to the sewer hookup. 
  • Put on rubber gloves and pull out your sewer hose. 
  • Screw one end of the hose into the sewer hookup in the ground. If the dump has no threading for this purpose, simply insert the hose end into the sewer hole and use some kind of weight to hold it in place (could be a large heavy rock, a tow dolly ramp, someone’s foot standing on it, etc).
  • Twist the other end of the hose onto the dump port on your RV. 
  • Pull the black water valve handle first and allow the tank to empty out through the hose and into the sewer hookup. Give it several minutes to fully drain.
  • Close the black water valve handle and pull the gray water valve handle second to allow the gray water to dump. Again, give it enough time to fully empty the tank.
  • Close the gray water valve handle.
  • Remove the sewer hose from the RV dump port, replace the cap on the dump pipe, and rinse out the hose using a water hose (but not your fresh water hose). A lot of dump stations will have a non-potable water hose just for this purpose.
  • Disconnect from the sewer hookup, replace the cap on the sewer hookup if there is one, and put your hose away. 
  • Wash your hands thoroughly, even if you wore gloves throughout this entire process.
  • Add a small amount of water to each tank (by running a tap and flushing the toilet a couple times) and pour tank treatment down a sink and the toilet. 

Maintaining RV Gray Water Tanks

Generally, the gray water tank is pretty easy to take care of. Simply avoid putting food, coffee grounds, and grease down your RV drains. It’s also a good idea to add tank treatment and a bit of water after each dump to keep the tank fresh between cleanings. Finally, you will want to keep an eye on the gray water tank roof vent to ensure the cap stays in good shape and no debris makes its way into the vent. 

Maintaining RV Black Water Tanks

Black tank maintenance is much the same as gray tank maintenance. A tank treatment and small amount of water after every dump will help keep things fresh, and the black water tank roof vent should be checked out once in a while. 

Additionally, you will want to make sure to use plenty of water when flushing and use only RV-specific toilet paper (which breaks down in your black tank more easily than the typical kind).

Finally, it’s important to avoid leaving the black tank open when hooked up to a sewer connection. Instead, only dump the blank tank when full and close it right away after. This helps ensure there is enough water in the tank to break down solids that could otherwise dry out at the bottom of the tank and cause problems down the line.

Keeping RV Water Tanks Clean

Following the steps above will keep your tanks clean enough for the most part. That said, you will definitely want to clean the tanks thoroughly once in a while. Below we’ve provided instructions on how to do this. 

Cleaning Wastewater Tanks

You will want to clean your wastewater tanks fairly often. Some opt to do this every time they dump their tanks, while others do it on a monthly basis. If you start to notice smelly tanks, cleaning should be the first thing you do to tackle the smell. 

Begin by dumping both tanks completely. Keeping your gloves on and leaving the sewer hose connected, follow the steps below to get your black and gray water tanks cleaned up and ready for your next camping trip. 

  • Put a clear piece into your sewer hose setup. This could be an elbow at the end of the hose, or a straight piece at the beginning or in the middle of the hose.
  • Attach a hose (again, not your fresh water hose) to the backflush inlet on the side of your rig. If you don’t have a built-in backflush system, consider an attachment like this
  • Open the valve to the tank you intend to flush (if you have a built-in backflush system, it might only flush the black tank).
  • Turn the water on and allow it to flush your tank, watching the clear piece of sewer hose to see when the water eventually runs clear. 
  • If your tank sensors have not been working, keep an eye on them to see when they read empty. 
  • When your sensors are working properly and the water is running clear, turn off the water. 
  • Repeat the process on the other tank if possible.

If you don’t have a way to backflush your gray water tank, you can clean it by dumping it and then filling it with fresh water and a ¼ cup of bleach for every 16 gallons of water. Let the bleach water sit for an hour or two before dumping the tank again. 

Some people will even drive around with a bit of bleach water in their black and gray tanks to help clean things up. 

Cleaning Fresh Water Tank

What about your freshwater tank? Yes, you only ever put clean water into it, but it’s still a good idea to clean the tank (and the rest of the system) from time to time. We recommend following the steps below at least once a year. We prefer to do it before our first camping trip of the spring season:

  • First, you will need to drain the system completely. Open all low point drains, let the water heater cool completely and drain it, and then drain the freshwater tank. 
  • Close all drains/plugs and fill the tank with bleach water. You should use about ¼ cup of bleach for every 16 gallons of water. Older RVs will let you pour the water into the tank using a funnel. Some newer RVs might require you to pour the bleach into a freshwater hose, connect to a potable water source, and fill the tank with water using the bleach-filled hose.
  • Pump the bleach water through the system by turning on your RV water pump and opening each tap and flushing the toilet until a small amount of bleach water has run through all. 
  • Turn off the pump and let the bleach water sit overnight. 
  • The next day, empty the system again by opening all drains (including the tank and water heater drains).
  • Close all drains/plugs and refill the freshwater tanks with potable water. 
  • Turn on the pump and run water through all taps until you no longer smell bleach. 
  • Empty the system one more time, making sure to replace drain plugs when you are through. 
Toilet paper

Getting Rid of Tank Odors and Clogs 

Even if you take perfect care of your RV water tanks, smells and clogs will happen from time to time. If this is something you’re dealing with, there are ways to get rid of the issue. Here are our suggestions:

  • Start by dumping and cleaning the tank using the instructions above. 
  • If you are still having issues, check the tank vents on the roof. Stick a water hose into the vent pipe and run water through it to ensure the vents aren’t clogged.
  • A worn toilet seal or ball can also cause issues. Make sure your toilet bowl is holding water. If it isn’t, it could be that the seal and/or ball needs to be replaced. 
  • Another problem that can cause smells and can even cause issues dumping? Solid waste buildup. Usually, this can be loosened up with a backspray tool. If you find this isn’t getting rid of the problem, you can try pouring boiling water into the tank or using a toilet snake to break up the buildup. 

Winterizing RV Water Tanks

In order to protect your RV’s plumbing system, you must winterize your trailer or motorhome. This involves filling all of the water lines with RV antifreeze or blowing them out so no water is left behind. It also involves getting the tanks ready for winter. 

To winterize your RV tanks, simply empty them out completely, leaving as little water as possible. Remove the drain plug on your freshwater tank and open all low point drains to ensure all water is removed. Clean your wastewater tanks thoroughly and dump a couple of quarts of antifreeze down both the black and gray water tanks to ensure anything left behind doesn’t freeze. 

For instructions on how to winterize the rest of your RV, be sure to check out this post

Repairing RV Water Tanks

Taking good care of your RV water tanks will help them last for years. That said, caring for your tanks doesn’t mean they’ll never break or crack. If you’re dealing with a broken water tank, you’re probably wondering what on earth to do.

In many cases, the solution is repair. Small cracks can usually be mended with a tank repair kit. Meanwhile, larger issues might be fixable with PlastiMend products.

If you can’t repair your tank, you might be looking at total replacement. While this is possible, it is pretty difficult, so you’ll want to be very handy and have plenty of tools on hand before diving in. Otherwise, a visit to your local repair shop might be in order. 

By now, you know pretty much all there is to know about RV water tanks. Use this information to keep your tanks in tip-top shape so you can continue to enjoy your camping experiences with as few tank incidents as possible!

This post contains affiliate links. RVshare may receive compensation if you make a purchase after clicking on a product or service link.

What do you think?

How much can you make renting your RV?

See How Much You Can Make

How much can you make renting your RV?

See How Much You Can Make

Similar Articles

Get Your Starlink First with RVshare

RVshare is pleased to help RV owners get fast access to Starlink for RVs. Starlink, a satellite internet constellation operated by SpaceX, has…

Read More

10 RV Laundry Hacks

One of the great things about RVing is that you can plan a long trip and you’ll have everything in…

Read More

5 Ways to Keep your RV Cool When it’s Hot Outside with AsoboLife

As summer rolls around, many of us are itching to get back into our RVs and travel all across the…

Read More

Keeping Your RV in Tip-Top Shape while Exploring the Country with Vanna Mae

Spring into early Summer is one of the most gorgeous times to hit the road and explore the country. I…

Read More

10 Underrated Destinations You Have to Visit!

Crowds at popular travel destinations around the U.S. seem to be increasing each year. Whether it’s thanks to beautiful pictures…

Read More

5 Ways to Enjoy a Rainy Day in your RV with Project Trek

While it’s not everyone’s idea of a fantastic family adventure, an RV road trip is a slice of Americana that…

Read More