Everything You Ever Wanted to Know About RV Holding Tanks

Modern RVs generally have three types of RV holding tanks. Here’s what you need to know.

RV holding tank
RV Plumbing System

Fresh Water Holding Tank

Freshwater holding tanks allow you to bring water along with you. If you treat your tank properly and are cautious when adding water to your tank, it’s perfectly safe to drink although many choose not to. That’s your decision. You can sanitize your fresh tank by using a sanitizing treatment specifically made for this reason. Some people choose to add a very small amount of bleach to the tank. I personally have not used this method but I’d do some research about safe amounts first.

When I am traveling I make sure to have at least a few gallons of water in my fresh tank to wash my hands and flush the toilet. I pull into rest areas for breaks but I use my own facilities.

When you are planning to dry camp you should determine whether you need to bring your water with you or if you can get it along the way. Water is very heavy. I have a 38-gallon freshwater tank. One gallon of water weighs 8.34 pounds. When my fresh tank is full I have added 317 pounds to my overall setup. I always consider the circumstances when making that decision.

Gray Water Holding Tank

The gray water tank holds your sink and shower water. Some larger RVs have two gray tanks. My gray tank, like my fresh tank, is 38 gallons. Our 5th wheel had 100 gallon fresh and gray tanks. The bigger the RV, the bigger the holding tanks.

Gray water tanks can get stinky and need some maintenance just like your other tanks. Dishwater often contains food particles and grease no matter how hard you try to prevent it from entering the tanks. Additionally, the drain plumbing can collect water and cause an odor. I also find when I am stationary for a while my gray tank’s odors are more likely. When you’re driving the water agitates the solids built up on the bottom of the tank and can be flushed out when you drain the tank.

The way I combat odors is to use some of your black tank treatment in your gray tank.

Black Water Holding Tanks

The black tank is where human waste goes. When starting out with a freshly flushed tank add a couple of gallons of water and whatever holding tank treatment you choose. I use Happy Camper. When your black tank reaches 75% capacity or more it’s time to dump. You can dump when it is less full if needed but you want the pressure of a full tank to help move the waste out more efficiently.

Gate Valve

Make sure you flush with plenty of water. If you don’t, you may end up with the dreaded poo pyramid. The water and holding tank treatment help it all break down into a consistency that is easier to flush.

How a black tank flush works.

When it’s time to dump your black tank, hook up the flush hose if you have a built-in flush, turn on the water, and with the gray valve closed, open the black tank valve. Allow the tank to drain and flush water to wash out the solids. Turn off the flush water and wait for the tank to stop draining then close the black valve again. Add more water. I often go inside and watch the tank level indicator.

I like to get the tank about 50% full before I open it again. Continue this process until the water draining from the tank is clear. Shut off the water, close the valve and release the gray water. Always add a couple of gallons of water to the black tank along with your holding tank treatment.

The gate valve handles are located outside your RV or in an exterior utility bay.

A note about holding tank level monitors. There are two main types of monitors, internal and external. Most RVs have an internal style. As you can imagine they get caked with debris and read incorrectly. Both of my previous rigs had internal sensors and I could dump and thoroughly clean my holding tanks but they would still read full or partially full. My Airstream had external sensors and it is quite accurate. I will never understand why the entire industry doesn’t use them.

RV Holding Tank Tips

  • Never leave your black tank valve open to drain freely. The only time it should be open is when you are flushing it.
  • It’s okay to leave your gray tank open when you have hookups however, you should close the valve and let it fill before you flush your black tank so you can rinse out your sewer hose after you finish flushing the black tank.
  • Never open the gray tank and the black tank at the same time. Waste can backflush into the gray tank and cause odors.
  • Never use your freshwater hose to flush your black tank and never use your black tank flush hose for freshwater. This contamination can make you very ill.
  • It’s always a good idea to clean the hose connections for your freshwater. I keep a can of disinfecting spray in my outside storage bay. I spray the connections and wait for a couple of minutes before hooking things up.
  • Wait for your tanks to stop draining before closing the valves. Bits of waste can get caught in the gate valve and cause them to leak. That’s nasty.
  • It’s better to travel with either a small amount of water or a completely full freshwater tank. A partially full tank will slosh when you are on the move and a large shift in weight at the wrong moment can cause some trailer sway.

Water and gravity are your friends. Use common sense and keep things clean and disinfected.

You might also like, The RV Living and Travel Guide For Beginners.

If you like this post, please pin it.

4 thoughts on “Everything You Ever Wanted to Know About RV Holding Tanks”

  1. Pingback: How to Boondock and Dry Camp Successfully - She Can RV

  2. Pingback: I Put This RV Black Tank Cleaner To The Test - She Can RV

  3. Such helpful advice. I wish I had this blog when I first started out :). While we do eventually learn by trial and error being armed with knowledge and doing it right the first time is so.much.better :).

    1. juley.torkomian

      Thanks Heather! I wish I had know all this too. It’s the funny little tips you pick up that are most useful.

Leave a Comment

Your email address will not be published. Required fields are marked *

Scroll to Top