What Are RV Holding Tanks and How Do They Work?

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After purchasing your RV you will probably be filled with excitement. There are so many things that you can do. You could travel across the country, go to a national park, or visit a beautiful campground that you have never seen before. However, before you do any of those things there are a few things you need to learn about your RV.

You see, RVs are more complicated than regular vehicles. There is a lot more to manage, and as a result, there is more you need to do to ensure that everything is working correctly. So, you will need to learn a little more before you can safely begin your travels. As you are probably aware, there are three major RV holding tanks. You will need to understand what they are and what each of them does before you start your first trip. 

So, what are RV holding tanks and how do they work? There are three major RV holding tanks. There is the fresh water tank, the black tank, and the grey tank. Each serves a different purpose and requires a different type of maintenance. It is not overly complicated, but you will still need to make sure that everything is running effectively and you do everything correctly. 

We know you are excited to get on the road and get your first family road trip started, but there are things you need to learn first. If you start an RV road trip without knowing the ins and outs of your vehicle, you will not have as good a time as you could if you did. So, take the time to learn about your RV holding tanks, and you will be better prepared for trips going forward. 

What Is an RV Black Tank?

There are two waste water RV holding tanks built into every RV. One of these tanks is the black water tank. The black water tank is the tank that catches waste water from your toilet. This tank allows you to use the facilities without needing to worry about being hooked up to a sewer connection at all times. 

Black water tanks collect liquids and solids, so you do not need to worry about separating any waste. It will collect human waste, toilet paper, and water that is flushed down the toilet.

What Is an RV Grey Tank?

Your grey water tank is the other of the two major waste water RV holding tanks. It is responsible for collecting all the waste water that does not come from the toilet. So, it collects water that comes from showers, and sinks. So, if you are cooking, washing dishes, showering, or doing any other water related activities other than going to the bathroom, the water will go to the grey water tank. 

What Is an RV Freshwater Tank?

While the two RV holding tanks we discussed previously are for holding waste, the third serves the opposite purpose. When you are out on the road, you will have a need for clean water. However, since you are not going to be hooked up to water like you are at a house, you need an easy way to access it. As a result, most RVs are built with a freshwater holding tank.

The freshwater holding tank holds all your freshwater. This water can be used as drinking water. However, it is not just used for that purpose. It also holds the water that comes from all your taps in your camper. It holds water that comes from your shower head, sinks, and anywhere else you get water. You use this water for bathing, cleaning dishes, and drinking water. It is a crucial holding tank that improves your overall quality of life. 

What Are RV Holding Tanks Made Of?

Unfortunately, there is not one type of material that all RV holding tanks are made of. However, many marine holding tanks are made of Low Density Polyethylene, also known as LDPE. This is a milky white plastic that is used in most freshwater tanks. There is also a milky grey plastic that is used in some holding tanks. 

That being said, not all holding tanks are made of the same material. As a result, you will need to figure that out yourself. It may be displayed on the tank itself. If that is the case it should be easy to figure out. In the case that it is not displayed on the RV holding tanks, you can check with the dealer or manufacturer. The dealer should have that information available to you. So, you can figure out the material that your RV holding tanks are made of with ease. 

Where Can You Dump RV Holding Tanks?

There will come a point where your waste water tanks will get full and need to be dumped. However, you cannot dump them anywhere you like. Dumping waste in a random area could cause damage to the environment and is illegal in many states. As a result, you will need to dump your RV holding tanks at designated dumping sites. There are many places that may be equipped with dumping areas.

If you are at an RV park or campground, they will more than likely have an area for dumping. In many facilities this service is included in the nightly fee. If it is not you will need to pay a service charge. 

Additionally, there are some truck stops and gas stations that are equipped with dumping facilities. It is even more likely when they are located near recreational areas. However, having a dumping area is not guaranteed so it is best to call ahead and check. 

Furthermore, you may be able to find RV dealerships with dumping areas. However, you will need to pay to dump at these locations.

There are some sporting goods stores like Canadian Tire that also may be equipped with a dump station. However, this is far less common than some of the options listed above. As a result, you may not have this option available to you. 

There are several other locations that may have dumping areas that you can utilize. However, which areas have dumping areas vary from region to region. As a result, you will need to do a little research to figure out which options you have available to you. It is always a good idea to know where you can dump your RV holding tanks before you leave for a trip. Not knowing could lead you to some unfortunate circumstances. 

How Do You Empty RV Holding Tanks?

So, you know where you can dump your holding tanks, but how do you empty them, and how do you know when they need to be emptied? Fortunately, most RVs are built with an onboard sensor system. It will check the levels of each tank and let you know when it is getting full. However, if you have an older RV it might not have these sensors and you will need to check the levels manually. 

Once your tanks start to get full, you will want to dump them. To do this you will need to go to the outside your RV to the section along the sideboard where the waste tank valves are located. You will see two valves, one for the grey water and one for the black water. You should then attack a sewer hose to the waste water outlet and ensure that it is tight on both ends. The other end should feed directly to the dump site. 

Once both ends are tightly connected, you can open the valve of the black tank. It is important to always dump your black water tank first. You do this so the hose can be washed out by the relatively clean water that comes from the grey water tank. 

When you hear the black water tank start to trickle to a stop, you can start to empty the grey water tank. Then wait until it is fully empty. Once the grey water tank is empty, close both valves.

If you need to fill your freshwater tank, you can fill it from the city water source at its inlet. It is a good idea to use a potable hose for this process as it will remove any strange smells or tastes from the water. 

How Do You Clean RV Holding Tanks?

Considering what is in your waste water tanks, you will probably want to clean them every once in a while. You also may end up in a situation where you have a clog. If this is the case you will definitely need to clean your RV holding tanks. Fortunately, holding tank cleaners and chemicals are very effective these days. So, you should be able to break down and clogs and leave your holding tanks smelling fresh with ease. 

To use cleaning chemicals you take the recommended amount, put it in the toilet, and flush it. There will be a recommended amount of water that you should flush it with that you should adhere to. Chemicals are available in liquid and powder form. We use Aqua-Kem RV Holding Tank Treatment in our RV and we think it works great!

Conversely, if you want to clean your grey water tank, you can use deodorizing chemicals. However, it is not always necessary to clean grey water tanks because they do not get as smelly as the black water tank. 

If you do have a tank that has an odor, run the water until you smell the bleach and wait at least 24 hours before you drain the bleach water. 

You may get in a situation where a clog is not decomposing. Although this is rare, it can happen if the clog is quite large and left unattended for a long time. If that is the case you can purchase a rinser such as the Rhino Blaster. You can use this device to directly jet water towards the clog at a high speed. This should help loosen up the material that is clogging your tank. It should clear up the clog for you relatively quickly.

Just be sure you buy the RhinoBlaster with the gate valve or it will not work correctly. We use our RhinoBlaster to rinse our tanks almost every time we dump. We think it’s a great product and we highly recommend it. NOTE: Never hook your fresh water hose up to the RhinoBlaster.


For a step by step method to clean your holding tanks and maintain them check out our article called How to Flush and Clean RV Holding Tanks.

How Do RV Holding Tank Sensors Work?

As we mentioned above, many RV holding tanks are equipped with sensors. These sensors will let you know when the tanks need to be emptied. However, some people will be more comfortable if they know how they work. So, how do RV holding tank sensors work?

Most RV holding tanks will provide you with a reading at four points. These four points are empty, one third full, two thirds full, and completely full. A traditional tank sensor will complete a circuit in a low voltage system. They are mounted along the sidewall of the holding tank so that the head of each sensor is on the inside of the tank. The sensors physically ascend in a line on the body of the holding tank. 

Once the material in the tank has passed a sensor, it will ground each sensor. When this happens a light will be displayed on the outside of the RV holding tanks. This way you will know roughly how full the tank is at all times. 


To learn everything you need to know about cleaning your black tank and it’s sensors check out our article called RV Black Water Tank and Sensor Cleaning Tips.

How Do You Keep RV Holding Tanks from Freezing?

Many people enjoy taking their RV out during the summer and enjoying the warm weather. However, that is not enough for some people and they want to experience living in their RV during the winter. This is possible and a great experience if you prepare for it. However, there is a lot of preparation required. Some of that preparation involves ensuring that your RV holding tanks do not freeze. 

To ensure that your RV holding tanks do not freeze, you can use non-toxic antifreeze that is specifically made for RVs. RV antifreeze is distinguishable by its pink coloring as opposed to the classic green color. 

To use antifreeze you will need to first completely empty your RV holding tanks and close the dump valves. You will then add a couple quarts to your black water tank by pouring it down the toilet. You will do the same for the grey water tank by pouring down the shower drain. The exact amount of antifreeze you need is dependent on the size of your holding tanks. 

You also need to keep in mind that waste will eventually dilute the antifreeze to the point where it loses effectiveness. As a result, you will need to empty your RV holding tanks more frequently during the winter. Every time you empty the tanks you will need to add antifreeze again. So, you need to keep an eye on the temperature of your tanks during the winter. If you notice the water temperatures are starting to drop, it might be time for you to empty your tanks and add new antifreeze. 


For a deep dive into keeping your holding tanks from freezing check out our article called How Cold Does it Have to Get Before RV Pipes and Tanks Freeze?

Hit the Road with a Full Understanding of Your RV Holding Tanks

After reading, we hope you have all the information you need about RV holding tanks. We know there is a lot of information to absorb, but it should all be helpful as you prepare for your future vacations and road trips. Your holding tanks are very important to your everyday life in your RV. So, having a full understanding of how they work and how to maintain them is very important. 

Remember, you have three major RV holding tanks. There is the black water tank which is responsible for holding waste water from your toilet. There is the grey water which holds water that has been used in your sink and shower. Finally, there is the freshwater tank which is used to store all your freshwater. 

The maintenance you need to do for your RV holding tanks may seem like a lot at first, but it is very manageable. Once you start doing it, you will realize that it is all quite simple. It is just a matter of learning how it all works and doing it correctly.  As long as you know what you are doing and you do everything correctly, you should not have any problems. 

Have you ever needed to dump RV holding tanks before? Are you a new or experienced RV owner? Are you interested in using your RV during the winter? Let us know in the comments!

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3 thoughts on “What Are RV Holding Tanks and How Do They Work?”

  1. If you have an auxiliary tank and a fresh water tank does that auxiliary contain black or gray or both?

  2. Your commentaries are great. I just bought a 2005 Alfa Gold and it’s so much to learn. I’m willing to pay someone to spend a day showing me the does and dont’s. I’ve talked to five RV owners and they all have different answers to how they set there RV up and what to cut off or leave on. You all are appreciated.


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