A Comprehensive Guide to RV Holding Tanks

Updated on January 2, 2018
Don Bobbitt profile image

Don has been an avid traveler and motorhome owner for most of his life.


This article is designed to help the RV owner understand the proper methods for efficiently dumping and cleaning holding tanks. I will also cover the different kinds of tanks, how they are used, and how to manage them.

The Three Main Storage Tanks in an RV

As all experienced RV campers know, there are three main storage tanks in a camper or motorhome. These tanks are:

  1. Fresh water
  2. Gray water
  3. Black water

These holding tanks make the RV camping experience a lot more civilized than, say, a trip into the woods with your backpack.

But along with the conveniences of having fresh drinking water, a hot shower, and a sanitary place for you to go to the bathroom, there are certain responsibilities you need to be aware of in order to keep your travels pleasant.

This diagram illustrates a typical RV holding tank system.
This diagram illustrates a typical RV holding tank system. | Source

Fresh Water Tank

The first and generally the largest holding tank is the fresh water tank. It is designed to store and provide fresh water. The size of this tank varies with the design and type of camper.

A pop-up camper or small tag-along might have a tank in the 10 to 20 gallon range, and is generally designed to provide enough fresh water for a couple of people to cook, drink, wash dishes, and possibly shower.

A large class-A motorhome or coach can have a fresh water tank with a capacity of 100 gallons or even more.

How to Take a Military Shower to Conserve Fresh Water

A military shower is a way to bathe that conserves your fresh water supply. To take a military shower:

  1. Step into the shower.
  2. Turn the water on and soak yourself.
  3. Turn the water off and soap up your body and hair.
  4. Turn the water on and rinse off.

This tried and tested procedure is the most efficient way to bathe to conserve fresh water.

Monitoring Fresh Water Quality and Pressure

The quality of fresh water around the country, specifically at campgrounds, can vary dramatically. By utilizing the items listed below, you can monitor the quality of your fresh water, ensuring it is safe to use.

  • Water filter – Always use a water filter in your water input line. Many RVs have a basic water filter installed already. These filters are there to block sediment particles and provide a better, charcoal-filtered taste. Some campers purchase another water filter and attach a short piece of hose to it. This way, the water is twice-filtered, and if there is sediment, it will gunk up the cheaper, stock filter, not your high-quality one.
  • Water pressure restrictor – Many campers are not aware that with every campground, the water pressure differs. Most of the time they only notice the change in pressure when it is too late and they are stuck with a shower head that only dribbles a few droplets of water at a time. On the other hand, too much water pressure can be dangerous. For these reasons, it is a good idea to purchase a water pressure restrictor or regulator for a few dollars online or at your local outdoor store.

Monitoring the Growth of Bacteria in Your Fresh Water Tank

Campers should always take the appropriate steps to avoid the growth of bacteria in their fresh water tanks. Your tank is in a dark place and is usually warm and wet, making it the perfect breeding ground for bacteria if preventative measures aren't taken.

One method is to purchase chemicals in the form of pills or tablets to prevent the growth of bacteria in your water tank. All you have to do is drop the tablet into your tank every now and then to minimize, but not completely eliminate, the chance of bacteria growth.

The best way to avoid bacteria growth, though, is to regularly dump your tank to avoid letting the water stagnate. All campers and RVs have a fresh water valve, making it easy to dump water when desired, and most campgrounds allow the dumping of fresh water at any time.

Winterize Your Fresh Water Tank When Necessary

Depending on how often you use your camper, as well as when and where, you will need to "Winterize" your fresh water tank and water lines.

What is winterizing? The word comes from the fact that most people use their RVs in the summer time, and store them during the winter. To winterize is to outfit your RV for months of immobility.

You must decide when it is appropriate time for you to perform fresh water tank and water line storage procedures. If you live in your RV, you may never have to worry about winterizing.

Most RVs have a service center to make dumping holding tanks easier.
Most RVs have a service center to make dumping holding tanks easier. | Source

Gray Water Tank

Your camper or RV also has a gray water tank. This tank is designed to collect and store the water that goes down the sink, shower drain, and washing machine drain. Gray water is water that is dirty, but not as dirty as sewage, which is known as black water.

The size of a gray water tank varies depending on the type of camper or RV. Generally speaking, it is designed to carry up to one week of waste, assuming there are only two people occupying the motorhome's cabin. It is possible to make a gray water tank last longer, but you must be sure to minimize waste by:

  • Taking military showers.
  • If you must wash your dishes in the sink, using the least amount of water possible.
  • When shaving, collecting the water required in a bowl or cup instead of using running water.

Dumping Gray Water

Regardless of how frugal you are, eventually you are going to have to dump your gray water tank. Campgrounds do not allow the dumping of gray water onto the ground. It must be dumped at a dump stations, the same place where you will have to dump your black water tank.

The dumping connections for gray and black water are the same for all campers and RVs.

When you look in the service compartment, you should see three-inch connectors. On most RVs, the lines link to T-type connections with one common three-inch connector.

These connectors are there so you can easily connect a three-inch flexible hose that is designed to connect to the dump station's inlet. This system is designed to minimize the opportunity for spillage and minimize cleanup.

Black Water Tank

This is where your sewage is stored until you have to dump it. RV owners learn quickly this is not a septic tank, but a temporary holding device for some extremely nasty stuff.

If you perform all the right steps, using the black water tank is not all that bad. But if you neglect it, a number of unsavory outcomes can occur, costing you plenty dollars and (s)cents.

A black water tank is designed to hold two individual's excrement and toilet paper for about one week. By following the tips below, you can make maintaining and dumping your black water tank easier on yourself and your nose.

Purchase RV-Friendly Toilet Paper

The toilet paper you use in your camper must meet certain standards. When purchasing toilet paper, be sure the package says "safe for septic tank or RV use" somewhere on it. This means the paper breaks down quickly. I also recommend purchasing only single-ply toilet paper.

One great way to make sure your toilet paper is RV-friendly is to test it. To do this:

  1. Place a few sheets of your chosen toilet paper in a cup of water.
  2. Wait an hour or so.
  3. After an hour has passed, cover the cup and shake it.
  4. The paper sheets should be shredded into pieces. If not, it probably won't breakdown in your black water tank.

Utilize Toilet Chemicals

If you are experiencing odors from your tank when you flush your toilet, these can be greatly minimized by using the proper chemicals. I will not recommend which chemicals to use, but whenever you dump your tank, pour a couple of gallons of water into it mixed with a chemical that is designed to catalyze the breakdown of the excrement. These chemicals come in pellets, powders, and packages.

Use Plenty of Water When Flushing the Toilet

This is one area of RV tank maintenance where you do not want to be frugal with water. When you flush, make sure a decent amount of water is also sent into the tank. This water will help keep the excrement soft and help the toilet paper breakdown.

The toilet in my RV has a foot pedal for flushing with two positions. If you hold it halfway down, water enters the toilet but does not flush. Once you press it all the way down, the toilet will flush. This allows you to manage the amount of water used with each flush. Make sure there is plenty.

Dumping the Black Water Tank

I will cover this more in depth later, but make sure to dump your black water tank first, close the valve, then dump your gray water tank. The gray water will help clean out whatever was left behind from your black water.

Flushing the Black Water Tank

Most RVs now have a tank flush system built-in. This is a water connector that connects to a hose with a shower-like head to spray the walls of the tank and the meter sensors.

Its purpose is to:

  1. Clean toilet paper remnants off of the meter sensors.
  2. Clean residue from the walls of the tank.
  3. Breakdown excrement and toilet paper remnants that may have hardened on the bottom of the tank.

Tank flushes work to a degree, but they are not perfect.

Hook-up Your Sewage Connector at the Campsite

When you pull in to a camp site, one of the first things you should do is hook up your sewage connector to the one provided. Even though you have it hooked up, do not open the valve until the tank is full. You should never let the sewage flow straight from the tank. If you do this, the waste will harden due to a lack of water, and you will end up having to pay for a very expensive pressure cleaning job.

Fill With Fresh Water When Not Being Used

When many campers are leaving a campsite to head to another site, they will dump their black water tank and fill it with water for the trip. This allows the water to shake and slosh around while they drive, and can really help clean the tank.

The same method can be used if you have a longer drive. Simply make sure to only fill the tank with about 1/2 to 3/4 of water, so that it has room to shake and slosh. If you won't be using your black water tank, this is a great, passive way to do some cleaning.

How to Dump Your Holding Tanks

A fellow RV owner once told me about an interesting way to dump your black and gray water tanks, rinsing your black water tank at the same time. He attended a class at a campground where he learned a new method of dumping, which I am going to share with you now.

Most RVs have only one outlet for both the black and gray water tanks. Also, most RV owners use a macerating sewage pumping system, similar to the popular sani-flo system, when dumping their tanks.

This setup allows one to use their gray water, including the detergents and soaps within, to clean the black water tank. How? Like so:

  1. Make sure all of your hoses are connected properly.
  2. Open the outlet valve and dump your black water tank as you normally would.
  3. Leave the black water tank valve fully open and open the gray water tank valve.
  4. The gray water will surge into the black water tank, stir up, and clean out all of that hardened mess accumulated on the walls and bottom of the black water tank.
  5. Close the gray water tank valve and wait a few minutes to let the detergents and soaps soak the black water tank.
  6. After 10 minutes or so, drain the black water tank again. You will be surprised how much foul water will come out of it that didn't get expelled on the first dump.
  7. Close the black water valve and dump the remainder of the gray water to clean your pump and exit lines.

Repeat this process regularly and you will keep your black water tank clean for a longer period of time.

Note: If your black and gray water tanks are the same size, you could theoretically perform this method of dumping twice: once with a 1/2 tank of gray water, and a second time with a 1/4 tank of gray water, a 1/4 tank of gray water to clean your outlet hoses.

Regardless of whether you do this or not, you still need to add activator/cleanser to your freshly dumped black water tank, as always.

How to Dump Your Black Water Tank (Video)

© 2010 Don Bobbitt


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    • profile image

      Peter 15 months ago

      Thank you. Best advice and how to.

    • Don Bobbitt profile image

      Don Bobbitt 4 years ago from Ruskin Florida

      Gmunson- That is a good idea but do it with caution. I had a friend who put far too detergent into the tank and about anhour into his trip, his wife walked into their toilet and found a toilet with a nice head of suds on it.

      But, you are right, it is good to get that tank cleaned as best you can.

      Thanks for the Read and Comment,


    • profile image

      GMunson 4 years ago

      Also it helps to fill your Black Tank with 5 Gallons of Hot Detergent Water before hitting the road. The steam from the hot water will reach areas that water containment may never touch. Then drain your water after it's agitated road run.

    • Don Bobbitt profile image

      Don Bobbitt 6 years ago from Ruskin Florida

      Jim c- interesting proposal,and it would of course provide some good agitation in the tank as the Ice beats around in there, BUT! And the but is, after you take your RV, whether a Coach or a trailer, down the road for 5-6 or more hours,and finally pull into a campsite , and then hook up your electric, water, sewage and then have dumped your tanks, you really don't want to unhook everything and pull out of the campground, just to get a little extra residue out of your tank.

      there are a lot of great ways to camp, but I really think that you will find that most RVers want simple solutions that fit into their travel plans with the least disruption. But, thanks for the suggestion. PS, the Ice idea works well in coffee pots!

    • profile image

      jim c 6 years ago

      If traveling, best way to clean Black water tank is, after emptying tank dump 5 or so pounds of ice and small amount of detergent in tank through toilet.Immediately start driving, after a few miles the tank will be completely clean.All the gunk will flush out at next emptying

    • Don Bobbitt profile image

      Don Bobbitt 6 years ago from Ruskin Florida

      Funny! But you're right, thinking back, they do work well on kids! LOL!

    • profile image

      Arlene V. Poma 6 years ago

      Wow, Don. I have friends who are lifelong RVers, but never did ask them how they cleaned their tanks. I think I'll stick with a campground (tent and bathroom within walking distance), Holiday Inn or timeshare. I am a klutz when it comes to these things. Reading your Hub was an eye-opener for me.

    • Don Bobbitt profile image

      Don Bobbitt 6 years ago from Ruskin Florida

      Thanks RV Guy, I did a cleanup of the original document and decided to re-share it with l\my followers, so thanks for the comment.

    • The RV Guy profile image

      The RV Guy 6 years ago from Somewhere In America

      Lots of good, basic information for the new RVer and a good refresher for those who have been on the road for a while.

    • Don Bobbitt profile image

      Don Bobbitt 6 years ago from Ruskin Florida

      You have to watch as the process begins, and as the flow from the Gray to the Black, slows, you quickly close off the gray valve, thus eliminating the potential back-flow.

    • profile image

      Steve 6 years ago

      What keeps the Black water from back flowing into your grey water tank?