RV Doctor: Short-term solution to prevent holding tanks from freezing


Dear Gary,
I’m currently driving through New Mexico in a Class C motorhome. Temperatures are running sometimes in the teens and 20s. Our RV is not equipped with tank heaters and we’re hoping you may have short-term suggestions to prevent damage to our holding tanks? —Mike

Dear Mike,
For a temporary trip through freezing temperatures, I would suggest simply evacuating the holding tanks and leaving them clean and dry until you can purchase tank heaters or drive out of the cold. Overnight in the campground, simply position a drop-light with a 60- or 100-watt bulb in the area of the holding tanks.

Add a gallon of windshield washer fluid to each tank as well. You could use standard RV antifreeze, but the windshield stuff is a lot less expensive. The fluid and that little bit of heat will allow you to use the tanks overnight and avoid potential freezing. Come morning, empty, flush and clean again until you get to a location above the freezing mark. Travel empty, use the windshield washer fluid and the drop lamp at night.

If your holding tanks are exposed under the floor of the RV, radiant heat from the highway might also be enough to keep the contents from freezing, so you might be able to go a few days with just the windshield washer fluid. Tank heaters, however, are still a wise investment if you hang around the cold country often enough!

gary-736Read more from Gary Bunzer at the RVdoctor.com. See Gary’s videos about RV repair and maintenance.


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I’m not an expert in Class C, but tend to think this would be a potentially viable solution.

To help offset some of that cold temperature (and assuming that you do have a furnace unit), consider using a 2″ metal duct into the basement area of those tanks. Just splice into one of the 3″ lines or use an open fitting on the furnace. A 1″ duct will take only a fractional amount of heat from the main cabin.

This should be able to keep the tanks plenty warm unless you are going into extreme temps.

Randall Davis

I would be more concerned about water lines freezing.

Brad Teubner

I have seen windshield washer fluid that says “protects to 32F”. Be certain to purchase fluid that protects to temperatures below what you will encounter.


Good point Larry. I have often wondered about the thinking involved with tank heaters as on our Cedar C there is some distance from the tank to the valves. At the valve, and the pipe to the valve is where ice damage can happen. A bit of ice forming in a near empty tank will never hurt anything.


INCANDESCENT light bulbs only… LEDs won’t work

Larry H Lee

Not all windshield washer fluid is formulated for use below 32 degrees. We are currently in south Florida and have noticed that all such fluid sold here even in the winter is only rated for use above freezing.
Also, unlike holding tank chemicals which require putting some water into the tank before adding the chemical, you should add the windshield washer fluid first so that it gets down into the discharge/ valve area to protect that from freezing.