The Ultimate RV Holding Tanks Guide – Read This First!

RV holding tanks are installed in every RV, for the purpose of holding three types of water. The first is the clean or fresh water, and the second is the water you use to shower or wash dishes, and the third type is commonly referred to as black water. This is waste water from the toilet. Any of these systems can cause problems if not maintained properly.


When the dealer sold you your RV, he most probably showed you around your new rig to show you: how to read the monitor to check for water levels, where the drain valves are and where the waste tank is.

But do you know how to fill and empty them correctly?

Fresh Water System

Yes, you need to fill the tank with clean water, but there’s more to it than just connecting a hose to the RV holding tank.

Only use a potable water hose to fill the tank. They are white in color and easy to identify.
If you decide to use a water hose, ensure that there is a pressure regulator attached. If the water is contaminated or smells bad, you can use household bleach to disinfect the RV’s holding tank.

  • Run the water until you smell the bleach, then let the tank sit for at least 24 hours after you have drained all the bleach water.
  • Refill the tank, then run the water again, until the smell of bleach is gone. You can then refill the holding tank as usual.

If the temperature is freezing, protect your hose. Install electric heat tape, if possible. High temperatures are just as bad as very low ones. Drain your holding tank often to prevent the water from stagnating.

There are different types of RV Holding tanks varying in size and design, depending on your RV.

Holding Tank Center End Drain HT703EDHolding Tank Left End Drain HT710EDHolding Tank Side Drain HT600SD
Waste Water System
Again, you would think, just open the dump valves and voila! holding tanks empty! Not so fast… doing this will actually be causing you major problems.

Firstly, municipalities require an odor tight connection. This is in the form of a special hose fitting, or a valve. None of which comes with the vehicle.

Sometimes, the dump sites are also located in such a way that it would be a hassle, or even impossibility, for you to drive to the site. This is where portable RV holding tanks come in handy.
Portable RV holding tanks are made specifically to make it easier for you to move waste water, and even fresh water, from your RV to the dump site.
They come in different sizes to accommodate the different-sized holding tanks.

25 Gallon Tote 4 wheel15 Gallon Tote 25 Gallon Tote22 Gallon Tote
Gray Water
Gray water is stored in its own holding tank. This is the water that comes from showering, cooking and washing dishes. No human waste is present in this water.
Some RVs have two gray water holding tanks.
The pipe that drains this gray water into the holding tank is very small, so try not to let food particles, such as peas or rice, go down the drain, or it will clog.

You can dispose of gray water, by using a hose in some vegetation. The gray water hose can also be left open to drain as it’s used, if you are connected to the sewer line.

Holding Tank Center End Drain HT620AEDHolding Tank Side Drain HT700SDHolding Tank Recessed Drain HT240RE

Black Water
This is the water that comes from the toilet, and only the toilet. Do not dump this water anywhere other than specific RV dump sites.

Never ever leave the dump valve for this holding tank open. This is because the water will drain away leaving a solid mess to accumulate in your tank.
The tank will fill, and your toilet will block. (Don’t do it!) Needless to say, if you do, this will be a nasty clean-up job.

Certain chemicals are sold specifically for black water tanks. They work to control odor, and break up solid matter, so as to drain easier. There is also special RV toilet paper that breaks down easier than your regular toilet paper. All this is done to try keeping your holding tank as blockage free as possible.

Remember, that lovely shiny monitor will not always work as great as it did when it was new, and may tell you you’re holding tank is only half-way full, when it’s actually close to bursting. Depending on how many people you have in the RV, set a schedule to dump the black water. It can be every other day, or once a week, whatever works.

Clean your black water tank often to prevent buildup. The easiest way to do this is to stick a garden hose in your toilet. Use as much pressure as possible. Black water holding tanks are usually immediately under the toilet, so this should work to flush the holding tank.

Holding Tank Bottom Drain HT630ABDHolding Tank Bottom Drain HT630BSBD

Holding tanks are by no means the glamorous parts of an RV, but they are a fact of life, and you will have to deal with them. Keep them clean, and your self-contained RV will be all the more a home while you are out on the road.

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