Friday, August 19, 2022


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 See Gary’s videos about RV repair and maintenance.



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1 year ago

Isn’t the problem the valves and not the tanks. If they’re not very full, there’s lots of room for the ice to expand. If they are full, that’s a lot of water to freeze–and it’s not pure water so the freezing point must be a little lower than 32°

2 years ago

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
2 years ago

I would be more concerned about water lines freezing.

Brad Teubner
2 years ago

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.

2 years ago
Reply to  Brad Teubner

What are they protecting from at that temperature?

2 years ago

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.

2 years ago

INCANDESCENT light bulbs only… LEDs won’t work

Tom Bird
2 years ago
Reply to  Fox

A 200 watt chicken coop flat panel heater is a little safer in the water bay.

Larry H Lee
2 years ago

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.

Bunky Beers
2 years ago
Reply to  Larry H Lee

Years ago when I was an avid skier we would take M/H to ski area for the weekend. Tanks never froze but those external valves always froze. Didn’t worry about it as when we descended the mountain they would thaw. On current Trek M/H I cut a hole in the bottom of the bathroom heat duct so heat from furnace now goes to tank area and my valves are now inside. I also have an electric, factory installed, heater in wet bay. However it is 12 VDC and will suck battery in a short time. It also gets quite hot so I am a little nervous about using it.

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