How Do I Prevent My RV's Holding Tanks From Freezing During Winter?

by Liz McDade
(BIloxi, MS)

I am staying in a MS campground and when the temperature drops to between 25 and 32 we were told to keep the dump valves cracked partially open and let the water run in a small stream all night to avoid freezing. Last night when I did that after first dumping a full tank of black, then gray - I awoke to the sound of water dripping and it wasn't the sinks. Somehow the black tank became full of water from what was running in the sinks and had backed up into the toilet bowl and was overflowing. I had to go outside and pull the valve completely open on the black tank - then all the water went down. Now I have a very wet bathroom carpet - out into the walking area.

Is this what I should have done? Without winterization, and living in an RV when the temps drop what IS the correct procedure. I was told here that if I left water in the tanks and the valves closed the tanks and/or the valves could freeze and crack. But I had also read that it was bad to leave both valves open because the bacteria from the black tank can get into the gray tank and I could be breathing it through venting in the sinks and shower.

Please help. It's a 1992 Europa and the holding tanks themselves are supposed to be double walled and insulated so I don't think the tanks would crack.

ANSWER Greetings Liz thanks for submitting your question on our Ask An RV Question Page.

I am really sorry to hear that you are going through this. Let's see if I can give you some suggestions on how to prevent this from happening in the future. Since you do not mention having any problems with the fresh water system in your RV we will just stick to solving the problem with the Black and Gray Water holding tanks.

You mentioned that your holding tanks are suppose to be double insulated and should not freeze. We are going to assume that they can freeze just to be on the safe side. Because if they do freeze and rupture; you are into a very expensive repair process.

I am assuming that you are hooked up to electric at your campsite and that you are running the furnace at night to keep some warmth in your RV. As long as the interior temperature of your RV remains above freezing, you should not experience any freezing problems in the faucets or interior drains.

I am not very keen on the idea of keeping the holding tank dump valves partially open to maintain a water flow going to the sewer, for the reasons you have mentioned above and because depending on how you have your sewer hose running from the RV to the sewer you could be setting yourself up for having an ice dam form in the sewer hose that could back up the gray and black water into the RV. I am not sure if that is what caused your most recent flood.

If I were you I would keep the sewer hose stored away until you have to use it to dump. Do not keep it hooked up all the time. The constant temperature variations could cause problems with the sewer hose, creating an even messier problem the next time you dump the tanks.

To prevent the gray and black water tanks from freezing you need to go out and buy some Non-Toxic RV Antifreeze which is designed for RV use. How much you will need depends on the size of your holding tanks. Once you get the antifreeze; completely empty the gray and black water tanks. Close the dump valves and store your Sewer Hose. Now add a couple of quarts of the antifreeze to your black tank through the toilet in your RV. Add another couple of quarts to your Gray tank through the shower drain. This antifreeze will also prevent your dump valves from freezing and protect your shower drain if it happens to be in a non-insulated section of the RV.

Dump your tanks frequently, do not let them get above half full before dumping them. Remember as the tanks start to fill up you will need to keep adding more antifreeze so the antifreeze does not become too diluted. Once you dump the tanks, just start the process all over again.

Some more permanent solutions to this problem would be to install a Holding Tank Heater Blanket to both of the holding tanks. A holding tank heater is like a large electric blanket that attaches to the bottom of the holding tank and plugs into a 120 volt outlet and prevents the tank from freezing.

I hope that the suggestions that I have given you will help in solving your holding tank problems. I urge our visitors to add their suggestions by clicking on the Click Here To Post Comments link at the bottom of this page.

Happy RVing

RVing Al

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