Monday, September 25, 2023


RV Education 101: RV black water holding tank tips

By Mark Polk

One thing lots of RV owners do not do is add enough water to the black water holding tank after the tank is emptied. Water is your first line of defense against odors and maintenance problems with the black water holding tank.

It’s helpful to know what size black water holding tank you have, because you want to add enough water to completely cover the bottom of the tank every time you empty it. A small RV holding tank might only need two or three gallons of water to cover the bottom of the tank, whereas a larger tank might require four or more gallons of water.

Fill the toilet bowl and add enough water to completely cover the bottom of the holding tank. After you add the water add the correct amount of holding tank treatment to the holding tank.

Motorhome RV Orientation®
Travel Trailer & 5th Wheel RV Orientation®

Mark Polk’s tech tips are posted every Saturday in the RV Travel Newsletter and every Wednesday on the RV Daily Tips Newsletter.



  1. My black tank is 3/4 full, has been for three months now & I probably will not be able to drain for another few months. (I just had shoulder surgery & virus shut my dump location). I re-loaded some treatment & some monthly water additions. No odor. Will it be OK to leave until I’m able to dump? 2005 Roadtrek 190 Any suggestions welcome.

    • I think you will find that the water will slowly evaporate [or quickly if you’re hitting 90 degrees]. Then you have a semi-solid mess that will be almost impossible to drain.

  2. I never fully empty my black or gray tanks. When the water coming out slows, I shut the valve. To me an empty tank, especially the gray tank, is an environment for a crusty mess. I do add additional water and treatment (Happy Camper) to the black tank immediately. And to the gray tank when it’s going to sit a while. But why drain it dry and then add more water back in?? Maybe I’m missing something??

    • The same theory might apply after you take a dump… after wiping your rear end a couple of times and the paper is almost clean, don’t waste anymore paper, your underwear will get the rest. I empty the tank and turn on the tank rinse for about 10-15 minutes and you’d be surprised how much “stuff” comes out afterwards which if left in the tank can cause sensors to quit working properly.


Please enter your comment!
Please enter your name here

This site uses Akismet to reduce spam. Learn how your comment data is processed.

Sign up for the

RVtravel Newsletter

Sign up and receive 3 FREE RV Checklists: Set-Up, Take-Down and Packing List.