RV Holding Tanks

RV Holding Tanks are installed in almost all RVs today to contain fresh water and gray and black waste. These and extra batteries make modern RVs “self-contained”. There are usually three main storage tanks in a camper or motor home. They are the Fresh Water, Gray Water, and the Black Water tanks. These holding tanks are great conveniences, but you must be knowledgeable, as well as understand the basic preventive maintenance that must be done to keep them working as designed.

Fresh Water RV Holding Tank

The largest of the three types of RV holding tanks is the fresh water tank. These are mostly made of a plastic material. They can be either black or white. The black color will inhibit the growth of algae. We find that the larger the rig, the bigger the holding tank. Small rigs might have as little as ten to twenty gallon capacity. We have a ninety gallon tank, and I have seen some rigs with as much as a hundred and fifty gallon storage.

Water weighs a little more than eight pounds per gallon. This means we are hauling more than seven hundred and twenty pounds of excess weight if we travel with a full tank. Fear not, we don’t do it. We put about a quarter of a tank in when we travel so we can flush the toilet with a little left for hand washing. There will be a valve somewhere close to the tank for draining the tank. I try to drain the fresh tank as often as possible to maintain fresh and clean water. Most campgrounds will let you do this on your campsite.

Gray Water Holding Tank

The grey tank is designed to collect and store the water that goes down the sink and shower drains and from a clothes washer if you have one. This water has soap and detergent in it but no sewage so it is called Grey Water. The tank is designed with a capacity that varies with the size of the rig. You should have enough capacity to hold up to a week’s worth of grey water from two people. This probably does not include use of a washing machine. The grey water tank is the biggest constraint to boon docking, or living off the grid without external utilities. It is usually almost equal or slightly larger than the black or sewer tank.

Campgrounds do not allow the dumping of grey water holding tanks onto the ground at a site. It must be dumped at the same Dump Stations as the Black Water tank. Dumping of Gray water when boondocking is a controversial subject. Some folks advocate dumping in arid areas to add water to the ground. I have no opinions on this.

To this end, the standard for grey water and black water tank dumping connections is the same for all campers and RVs.

When you look in the service compartment of an RV, or under a camper, you will recognize the same 3-inch connectors; and on many RVs, the black water and grey water lines go to a T-type connection with one common 3-inch connector. This is for ease of connecting and dumping of waste.

Black Water RV Holding Tank

The black water tank holds the water that goes down the toilet. Some rigs with two toilets may have two black tanks. I can’t imagine why, but there are some instances of a manufacturer building a rig with only one holding tank that contains the grey water and the black water. I’m sure this saves some money, but I don’t think the designer ever traveled and camped in an RV. Both the black and grey tanks will be vented to a fitting on the roof of the RV, just as a home plumbing system does.It is possible to get odors from that inside depending on whether the roof vents are open and the direction of the wind.

It is easier to clean out a sewer hose with soapy grey water than any other way. That’s why it is recommended that you dump the black water first, then the grey. Doing this will allow the grey water to flush out the waste that is left in the hoses from the dumping of the black water tank, and helps clean the hose system, leaving only (or at least mostly) Gray Water waste in the hoses.

In the chapter where I covered buying sewer hose, I recommended you have plenty to reach distant sewer fittings. This did not mean hooking all of them up and letting them flop around on the ground in a heap of coils that look like a resting boa constrictor. Use only as much as you need to make a straight run and elevate it off the ground with one of the many available types of plastic gadgets that look like slinkies made for that purpose.

When you check into a campground, you will be given material about the rules; often there will be a statement telling you to use a threaded sewer connector. Other instructions may tell you to use a rubber sewer gasket or doughnut to seal up the space between your sewer hose and the campground sewer connection. Please read these instructions and heed them as local ordinances direct these actions.

RV Toilet Paper

Here is the scoop on toilet paper for use in an RV. Unless you like to throw money down the toilet, don’t buy the expensive “RV” brand. Many other common brands work quite satisfactorily. What you need to know is that it will break down in the tank. To test toilet paper, place a few sheets in a covered cup of water. Gently shake it for a minute. Remove the top and the paper sheets should be shredded into pieces. If not, it probably will not break down in your tank either.

RV Black Tank Chemicals

There are probably hundreds of chemical products to put in the black tank. Most are to cut down on odors. Others add chemicals to help break down and liquefy the waste. Whatever you use, try to stay away from any product using formaldehyde. This is definitely an environmentally unfriendly chemical and will kill the beneficial bacteria in septic systems. Try to find an enzyme based product. We use a tablet type, but it also comes as a powder, liquid, and even a premixed, dissolvable pack. Unfortunately, these enzymes will not work in very hot or very cold temperatures. They also need more time in the tank than most of us have. We dump before the enzymes have had time to do their job. We solved the hot weather issue with a product called “Odorcon” which contains stabilized chlorine dioxide. This stuff works great. Check them out at http://www.3rodorcon.com/ . They also have a great product for your fresh water tank.

For most of the time we are using a method called the “Geo Method” developed by Charles Bruni. That method uses household water softener, detergent, and household bleach(in a very diluted form) as the solution to tank odors and fouled tank sensors. Check out this page all about the Geo Method.

Flushing the RV Toilet

When you step on that pedal, hold it down for a while. Most RV  toilets have another pedal position that will allow you to add water without flushing. If the flush contains toilet paper, fill the bowl with water and then flush. More water in the black tank will make it easier for the enzymes to work. 

Dumping and Rinsing the Black and Grey RV Holding Tanks

OK, you have set up your sewer hose, tightened everything up and have two full tanks. Let the fun begin. Not so fast. It is a wise person who plans ahead. When the black water comes cascading down that three inch hose, there is a lot of weight behind it. When it is turned loose, it could lift that sewer hose right out of the connection if it isn’t tightly threaded or weighted down with several pounds of weight on top of that end of the hose.

We spared no expense on this device. I found the worst and most stretched out pair of sweat socks I could find, filled each with gravel, tied them together, and draped it over the business end of the sewer hose. It’s hard to believe how much of that stuff will spread out on the ground and cover your shoes before you can close the valve. Whatever you want call it, this is nasty stuff. You may have heard this called the black water dance. Now you know why. The thing that an RVer learns very quickly is that this is not a septic tank, but just a temporary holding device for some extremely nasty stuff!

This tank was designed to hold the excrement, urine and toilet paper of a typical couple for about a week. Please do not put anything else down there. If you accidentally drop something you want to keep down there, rethink it. The complications and downright nastiness of a clogged black tank are not worth it.

Hopefully you purchased a short clear section of plastic sewer pipe attached just below the dump valve. This will allow you to see when the dump is complete and see the condition of the flush water.  Did I mention that you should wait until the tank is nearly full before you dump? Here we go. First you will want to pull the black tank valve handle all the way out. You will be rewarded by a rush of brown stuff followed by a gurgle. Hopefully, your rig is equipped with a built-in black tank rinse system. This is one or two nozzles plumbed into the side of the black tank to rinse out the interior. Hook a short water hose up to the rinse hose connection and start the water running. You will see all kinds of stuff flowing out of the tank you just dumped. Keep this up for a minute or so and then close the black tank valve while the water is running. This will start to fill the black tank with water. At this critical point, do not let yourself become distracted. This is because the black tank has a vent to let sewer gasses escape out of a fitting on your roof. If you forget to turn off the water, the tank will fill and there will be strange noises coming from the toilet. Do not step on the flush valve unless you want to be rewarded with an explosive shower. In short order, the water will start to rise through the vent pipe and provide you with a really good reason to clean your roof. Wait no more than about eight minutes for a forty-five gallon black tank and pull the black tank valve. The extra water will do a good job of removing stuck toilet paper from the sides of the tank. At some point, the clear section should show the water running clear.

At that point, the tank is clean and rinsed. Let several gallons of water run into the tank to coat the bottom with several inches of water. Close the black tank valve and open the grey tank valve. The grey water will run out as a solid stream and then finish with a rush of bubbles. A nearly full grey tank will do a good job of cleaning out the sewer hose. Now is the time to put the chemicals in the black tank.

RV Holding Tank Sensors

Until quite recently, the sensors inside the holding tanks were metal rods threaded through the side of the tank at intervals to indicate the liquid level in the tank. This works quite well in fresh and grey water tanks. Unfortunately, toilet paper remnants and other stuff will get hung up on these and the tank monitor will usually read much higher than what it really is. The only sure cure I know of is to have the tank professionally steam cleaned. The folks who do this have a video camera attached to the hose and they can find and remove all the remaining stuff in the tank. This costs around four hundred dollars for both the black and grey yanks and is the only way I know of to get those pesky sensors clean. Guess what? It won’t be long and they will be clogged again. Newer sensors are taped to the outside surface of the RV holding tank and are quite accurate. Retrofit kits are available that use existing wiring.

Holding Tank Hookup

At a Campsite

When you pull in to a campsite, one of the first things you will do is hook up your sewage connector to the one at your site. Even though you hook up, DO NOT open any valves until the tanks are full. If you dump a partially filled black tank, there won’t be enough volume to remove most of the waste. There was a time when we left our grey valve open all the time, but now we keep it closed until it is full. Typically we dump grey twice as often as black. We will do it more often when using the washing machine.  Please do not leave the black tank valve open all the time. The waste will harden due to a lack of water in the tank, and you will soon find out what we mean by pyramiding. You will eventually clog up the black tank and will have a very expensive tank pressure cleaning job to look forward to. Leave the valve closed, and open only when full and ready to be dumped.

On the Road

Some folks will leave a site and drive to the next campground in the same day. They will dump the black water tank and fill it with water for the trip. This will allow the water to shake around during the bumps and turns of the trip, and can then be dumped again when you arrive at the next site. This agitation during the trip can really help clean both RV holding tanks. We have heard that putting ice cubes down the toilet will help this agitation. Unfortunately, the ice will melt quickly. Another idea is to put about ten pounds of rock salt of the type used in ice cream freezers into the black tank. This should last longer than the ice.

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