Thursday, August 11, 2022


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.

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



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George J Herberger
2 years ago

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.

Tom Gutzke
2 years ago

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 years ago

Bob p,

Your response was funny- thanks!

2 years ago

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??

Bob p
2 years ago
Reply to  Arlene

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.

Raul W Smith
2 years ago
Reply to  Bob p

Bob I fully agree with your statement….

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