An Explanation of Your RV’s Holding Tanks

filling the water tank of a campervan in campground area

Plumbing and sewer systems are one of the many things that new RVers fear most, and understandably so. The last thing anyone wants to deal with or have an accident with is human waste. It’s gross.

With that said, you don’t have much to worry about. RVs have been designed to make it as easy as possible.

But I don’t expect you to take my word for it. Knowing a bit more about the holding tanks on your RV can go a long way towards demystifying your RV’s sewer system and eliminating any untrue preconceived notions about what it’s really like.

The Types of Tanks

Clean and wastewater tanks in a camper
Image from Getty

There are three different tanks on an RV. There’s the black water tank, the gray water tank, and the fresh water tank. Together, these three tanks give you everything you need. Two of them are for wastewater and one (I bet you can guess which) is for fresh, potable water.

Black Water Tank

The black water tank is for everything that goes down the toilet. This is the gross stuff. The solids and the liquids and toilet paper, and hopefully, that’s it. Other personal hygiene products and feminine hygiene products should not go down the toilet and into this tank. Doing so could cause a clog, which is the last thing you want when camping

Gray Water Tank

Your gray water tank is everything that goes down your sink and shower drains. It’s wastewater but it’s not quite as gross as what’s in your black tank.

Fresh Water Tank

The fresh water tank is exactly what it sounds like. It’s a tank for holding fresh, potable water in reserve. It’s the water you can access via your shower and sink. That water is also used to make your toilet flush and any other functions that need water.

RV Holding Tank Sizes

The size of the holding tanks on your RV will depend on the size of the RV. You’ll routinely find holding tanks from 15 to 40 gallons (gallons is how the size is measured). It just really depends on your RV.

No matter how large or small your RV’s tank sizes are, you need to keep track of how full your tanks are. Many RVs come with tank monitoring systems. While these systems can be helpful in my experience they’re not always 100 percent accurate, so it’s smart to just keep in mind how many days you’ve been camping and about how much water you have in your tanks.

The more time you spend camping the easier this will be. I’d suggest going on a few shorter camping trips and getting the hang of things and understanding about how much water you use each day before going on a long, extended trip.

Filling Your Fresh Water Tank

If you’re at a campground with a freshwater hook-up at your campsite, you’ll be using a city water inlet on your rig. This means the fresh water tank is not used. The water from the water hook-up goes directly into your RV’s plumbing system.

However, if you’re camping somewhere without a freshwater hook-up—maybe you’re boondocking—then you’ll need to fill the fresh water tank. There is a separate inlet for the water that will fill your fresh water tank. Your fresh water tank should be filled using a specific hose designed for potable water. It’s also a good idea to add a water filter to the hose before the water goes into your RV.

Basically, you will fill up the fresh water tank until you see that the tank is full or it flows out of the inlet.

Emptying Your Tanks

Man with RV vehicle in dumping station
Image from Getty

Throughout your camping trip, you’ll use the water in your fresh water tank and then that water will go into the gray and black water tanks. At the end of your camping trip, you’ll want to empty these tanks. Most campgrounds will either have a dump station for you to use or a sewer hook up right at your campsite.

It’s usually smart to wait to open the valves of your black and fresh water tanks until they are reasonably full. This way, there is enough liquid in there to flush out all of the gross solid waste.

While individual procedures for emptying your tanks will vary slightly from RV to RV, the general process goes something like this: connect your sewer hose equipment to your RV, connect that equipment to the dump station or sewer connection, open the valves to the tanks to empty them. Once empty, close the valves and you’ve successfully emptied the tanks.

Generally, it’s smart to open the valve on the black tank first and let it drain. Once it has, you can then open the valve on the gray tank. Why do it in this order? The gray water tank is going to be mostly dirty dish soap and shower water. It’s far less gross than what leaves your black tank and generally works well to flush out the sewer hose used when emptying the tanks.

If you have more questions or concerns about emptying your tanks, consider reaching out to your local Gander RV & Outdoors. The folks there will be able to show you exactly how to do things on your specific rig.

Maintaining Your Tanks

Keeping your holding tanks in good condition is imperative. Each tank has important maintenance steps.

First off, the black tank. This tank will require special sewer chemicals. These chemicals are available for purchase through Gander or you can go to any RV shop to find them. They help to deodorize what’s in the back tank and ensure that solid waste is broken down properly. Use your RV’s manual and the directions on the specific chemicals you choose to use to determine how much to add to your black tank. All you do is flush the chemicals with some water, so it’s really a very simple thing.

You will also want to flush your black tank from time to time. Some RVs come with special black-tank flushing systems, while others will require you to flush the tank from the toilet. Either is fine. Follow the directions in your RV’s manual to see how it’s done and how often to flush the system. Please note, though, that you should have a separate hose for this. Do not use the potable water hose you use in the fresh water tank.

The gray tank and fresh water tank will need less attention because of the nature of the tanks. However, it’s still smart to sanitize these tanks from time to time. Check your RV’s owner’s manual to see the recommended procedure for sanitizing your gray and fresh water tanks. While you can use a special sanitizer, I know many RVers who use household bleach to sanitize these tanks.

The general rule of thumb is a quarter cup of household bleach for every fifteen gallons of water. If that sounds like too much, do a little less.

Let the water run until you smell the bleach and then let the water sit in the tank for 24 hours. Once the 24 hours are up, open up the gray tank valve and turn on the faucets to let all the water drain out. From there, you should do a rinse of the system (possibly a couple of times) to ensure all the bleach has been washed away.

When it comes to making sure your gray water tank is in good shape, I wouldn’t recommend you let bleach water sit in the tank for long periods of time. Instead, look for a designated gray tank cleaner or use some dish detergent. Let the dishwashing detergent sit for 24 hours and then drain the tank. This should be enough to help clean the tank.

Have more questions about holding tanks? Head into your local Gander RV & Outdoors. Someone there will be able to help you understand all that you need to know. 

An explanation of your RV's holding tanks



  1. I do not agree with bleach. However. I have used the same treatment in 2 5th wheels for 23 years without issues and use fresh water treatment for the first outing in the spring. I usually leave the fresh water treatment in for 1 or 2 days prior to a trip but drain it and add fresh water just before leaving. For the waste water I like to drain the gray water before I leave a site but won’t empty the black water until the tank is 1/2 full. The agitation on the road tends to brake down any solids and the larger volume of liquid gives a better flushing. More recently I have been filling the fresh water tank at the end of a trip and this keeps the plastic taste out of the water, drain and add fresh for the next outing.

    1. Hi Bob, what treatment do you prefer? Do you know the brand? Just curious.

    2. What about adding fabric softener to the black tank does it help at all loosen up the sides

    3. Wonder at what temperature the blue water in the black tank freezes and if it can be left in during winter with no antifreeze if toilet was not used and if toilet drains right into black water tank. I have nowhere close to drain the black water tank blue water and do not know what the blue water is. Jyst bought the rv a few months ago and live in minnesota

  2. A better option to the tank drainage sequence is to open the grey water momentarily to check your lines and connection to sewer for leaks. It’s much more pleasant to have grey rather than back water leak out. Then if all is OK, drain the back followed by grey.
    This is especially useful if your system hasn’t been used in a while or if you don’t trust the campground sewer connection.

    1. Hey Robert. Great point! Definitely smart to check for leaks first.

    2. I do agree. This is a very import precaution to take, that I learned the hard way.
      The first time I used an RV dump, I hooked up my hoses went thru my check list, and nervously pulled the black tank release. Loud gurgling began and then almost immediately ended.
      It took awhile to diagnose, but eventually discovered embedded caps in the hoses. I shut my tanks back down, but still had several gallons of black tank that would contaminate the site in order to correct the problem.
      Horrified and thoroughly embarrassed, I then had to confront the disaster and clean up the area before continuing.

  3. Hi I filled my fresh water tank and went boondocking and after one day I land all of a sudden my fresh water smells like sewer real bad

    1. Hi Steven, it sounds like your freshwater was contaminated or there’s bacteria build up inside your tanks. Sanitize your tanks or have a service department do it, and it should eliminate the bacteria and thus the bad smell.

  4. My range hood light and fan do not work. Is this an easy fix?

  5. I drained my grey water tank but all of the freshwater in my holding tank also came out with it. Do I have a valve or something that’s open?

  6. Can hooking up to campground water when your fresh tank is full cause your grey tank to fill up?

  7. Should you bypass your water heater when sanitizing the fresh water tank?

  8. There is no place to put our sewer hose when traveling. we have a small toy hauler, ORZAK 1700 – Forest River. is there somewhere to put it under the body of the trailer? Where would that be?

  9. Wade I’m a full-timer & having to flush black tank every 4 days, smell knocks me down, however reason being is it doesn’t fully empty seems there be a clog.

    Have any ideas because I have tried many suggestions that don’t work.

  10. I am trying to winterize my small travel trailer. I found nothing that tells you how to do it. I bought the PINK stuff for winterizing. All the tanks are empty, but I did put some of the Pink stuff in all the drains, and toilet. What else? I had a motorhome at one time and we just put a hose in the pink stuff and turned on the pumps till the faucets all ran pink, never had any problems. Now what?

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