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A Comprehensive Guide to RV Holding Tanks for the Beginner

Don has been an avid traveler and motorhome owner for most of his life. He shares his experiences along with valuable tips for RV owners.

RV Holding Tanks

This article is designed to help the RV owner understand the proper methods for efficiently dumping and cleaning the holding tanks in a camper.

You can also see helpful information on the different kinds of tanks, how they are used, and how to maintain 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. Freshwater
  2. Gray water
  3. Blackwater

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.

Freshwater Tank

The first and generally the largest holding tank is the fresh water tank. It is usually designed to store and provide enough fresh water to last a little over a week of average use.

The size of the freshwater tank in an RV varies with the design and type of camper, but the tank size is generally designed to hold more than the GRAY and BLACK water tanks.

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 freshwater 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 freshwater around the country, specifically at campgrounds, can vary dramatically. By utilizing the items listed below, you can monitor the quality of your freshwater, 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 freshwater 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 freshwater 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 summertime, and store them during the winter. To winterize is to outfit your RV for months of immobility.

You must decide when it is an 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.

Class-A RV service center. Most RVs have a service center to make dumping holding tanks easier.

Class-A RV service center. Most RVs have a service center to make dumping holding tanks easier.

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 go longer before dumping it, but you must be sure to minimize gray water waste by:

  • Taking military showers.
  • If you must wash your dishes in the sink, use the least amount of water possible.
  • When shaving, collect 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 of dollars and (s)cents.

A black water tank is designed to hold two individuals' 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 break down in your black water tank.

Utilize the Best 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 break down.

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 of course, but they are not perfect.

Hook Up Your Sewage Connector at the Campsite

When you pull into a campsite, 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.

RV Tank Cleaning Trick

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 an activator/cleanser to your freshly dumped black water tank, as always.

This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.

Questions & Answers

Question: I think I have a leak coming from the connection between my house plumbing and the gray tank. I have a diagram of the plumbing, but it does not describe this connection. The manufacturer is Forest River. It is expensive to have someone fix this for me, and I was going to try to fix it myself. Can you help me understand the junction between the plumbing and the gray tank? Is this something a DIYer can do or should it be left to a service dept?

Answer: Your Sinks and Shower drains are what go to your Gray Tank in your RV. The plumbing is pretty straight-forward and they gravity feed to the tank.

You should be able to trace the pipes quite easily to look for a crack or loose connection.

Repairing this plumbing does require a certain level of experience/skill to do it properly though. So, if you have not done this before I recommend you take a class at your local Home Depot or Lowes before you get into doing this yourself.

Question: What is the best way to clean sensors in the gray water tank? I am a workamper so I am stationary for 5 months. I do wipe my dishes before washing but something must have stuck to one of the sensors as always shows 2/3 full when the tank is wide open.

Answer: I understand your problem. A lot of attention is paid to cleaning a Black-Water Tank, but people usually ignore the Gray Water Tank. Gray tanks do not have built-in showers and when something does get hung up on the sensors it can be a problem.

If you can imagine a piece of food hanging there on the sensor, you can understand your problem a little better. Eventually, you can hope for that piece of food to rot and fall off of the sensor, but too often the piece of food dries up and turns into something resembling a piece of jerky. When this happens it has shaped itself to hang there, on the sensor and considering it is high enough to be on the 2/3 sensor, it probably doesn't get wet too often so that it can soften and fall off.

Considering all of this useless information, there is one trick you can try.

Fill your Gray tank up to where you estimate the sensor would be, let the water sit for a day or so, and then drive the Rv up and down the road to hopefully allow the sloshing water knock the piece of food off of the sensor.

This isn't a new trick. In fact, a lot of people have this problem with their Black Water tank and they do the same thing but they will add a couple of bags of ice cubes down the toilet and hope the ice knocks the toilet paper off of the sensor when the built-in shower doesn't work.

PS. Keep that trap in your sink. You will be surprised what gets caught before it goes down the drain.

Question: How do you fill your black water tank for driving or cleaning purposes?

Answer: You never fill your black water tank. I recommend that you dump the tank then add some water before you hit the road so that the shaking will break up any sewage that has solidified in the tank, then flush the tank when you get to your next campground.

Question: I moved into my camper a year ago and I made the mistake of leaving my black water plug open and now it's not draining what can I do?

Answer: This is a regular mistake made by many RV owners. Your black and gray water tanks along with your hose system IS NOT designed to act like a Home system. They will eventually clog up!

And that sounds like what you have, There are some things you can try such as; “kick” or move the drain hose in the hope the dried up sewage breaks up and flows out.

Otherwise, you may need to disconnect the drain hose (Yuck) and throw it away, hoping that the tank is not totally blocked also.

Then you need to regularly (weekly?) dump and drain that tank hoping to break up the dried debris over time.

Eventually, you can hope you can get back to a regular tank dumping regimen.

Also, depending on tour finances, many campgrounds have the address of specialists who will come to your camper and use a steam pressure system to clean your tank properly.

Question: My RV has a toilet with a right foot flush. The middle lever of the three that are under the trailer dumps the black tank. The other two only pull out halfway, and seem to do nothing. So what are they for?

Answer: From what you have told me; and your Rig being a small trailer camper, the manufacturer may have used a standard assembly across their line of products to save money.

As I mentioned before, your camper may only have one waste holding tank and dump their Gray and Black waste into one tank. A freshwater tank will usually have a separate dump valve to allow the user to clean out the fresh water tank for storage, but I know of NO manufacturer which would put the fresh water tank dump connector near the Black, or even use the same dump hose, for fear of contaminating the clean water.

Short of crawling under your camper and tracing the hoses to see where they go, I would guess that you have only one tank and dump for both Black and Gray water, as I said.

Question: I purchased a trailer that is used only seasonally. It has three pull valves, and only the middle one pulls out. Can you shed some light on this setup? I read that some RVs only have one tank. Is this the case for me?

Answer: An RV will typically have three tanks; Fresh Water, Gray Water, and Black Water. The Fresh Water tank usually has a drain valve to empty it and avoid it being damaged by freezing temperatures in the winter. The Gray Water tank which holds Sink and Shower drainage is used to dump the tank, normally using a standard 3-inch diameter sewer hose. The Black Water tank holds the toilet residue and is dumped using the same sewer hose.

So, the question for you is, do you have a toilet? Some trailers just use a porta-potty and thus do not have a Black Water holding tank.

Question: What is the best way to seal the junction between the black water tank and dump tube?

Answer: Typically your Black and Gray Tanks are connected via a Selector Adapter. This device allows the user to select which tank is being dumped.

If you have a leak at the junction of this adapter and the black water tank, it usually has a "rubber ring" that seals this junction.

If it is leaking at this ring then you could get a new ring if you contact the Customer Service office for the manufacturer and get a price.

But, most people would probably just order a NEW adapter assembly. Take care though, because there are a number of physical configurations that are made to fit in the space available of certain RV's.

Question: If a camper is hard plumbed and I have an electrically heated hose, is the maintenance of holding tanks required especially in winter? Also, does the PVC hard plumb need insulating?

Answer: It is not recommended to hard plumb the sewage from your RV to a septic tank unless you can replumb everything straight to the external plumbing. The buildup will eventually cause some serious cleaning problems. Most people who hard plum their RV to an external system will still utilize their holding tanks, and regularly dump and clean them, both the Gray and the Blackwater tanks. Then everything will work well for you through a year or two.

But constant flow through the holding tanks, to an external line, will eventually have buildup and get blocked.

And, yes, if you use an external drain pipe, it should be insulated or use a length of heated tape to keep it from freezing in cold temperatures.

Question: I have always used liquid bleach diluted in a bucket of water when dumping. After dumping, rinse your hose by placing it in the pail and all connections and rubber gloves. Then before leaving pour the water around the sewage dump basin and in it. Have you heard of using bleach as a method to keep bacteria away from an RV's holding tank?

Answer: Of course, Bleach is a good chemical to use when cleaning your sewage hose after draining it.

In addition, I would recommend that you store your hose, any adapters, gloves, and such equipment in a sealable plastic container as a secondary measure of preventing any accidental contamination. This has worked for me for years.

Question: Inherited a fifth wheel which a full, dry blackwater tank. How do I clean this?

Answer: Your problem can be hard to clear up, but let me give you some suggestions. Pour a large dose of the chemical used in Black Water Tanks to help break things down, and then pour Ice Cubes in the tank. Once done, drive the camper for 10-15 miles and let the ice shake around and hopefully break up more of the poop. Then let the ice melt and drain the tank.

You may have to do this several times.

The only other way to take care of this kind of problem is to hire one of the professional tank cleaners that you can often find serving local campgrounds. They use high-pressure steam and essentially break up the Poop and then clean out the loose debris.

On another note, always make sure you are using toilet paper that is designed for septic tanks and camper tanks because it breaks up quickly when wet.

© 2010 Don Bobbitt