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Old 08-21-2004, 01:22 PM   #1
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Frozen Holding Tanks

At what temperature will a holding tank freeze? I know the scienific answer, but need the practical answer for trailers.

Fresh water is above the floor, black is suppose to have a heat vent on it (hope it is there, cause I can't see it!), grey is not heated. Will be out in the wilderness next month. Weather there is already in the thirties at night. When do I have to worry about the grey tank freezing? Should I put RV anti-freeze in it? How much? It is a 18 gallon tank.

Advice is appreciated!


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Old 08-21-2004, 03:17 PM   #2
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If I understand you correctly, you're going to tow the trailer somewhere next month and then stay in it, away from hookups. The most likely time for the tanks to freeze will be while towing, not while you're living in the trailer and keeping it warm. So make sure you dump the tanks before you head home.

An empty tank (or at least one that is 95% empty) doesn't present a freezing issue and doesn't need antifreeze.

If your question is really "When will a tank in use freeze?", there really isn't a specific number. The vents that heat the black tanks lower the outside temperature at which you can use the tanks, but nobody is going to certify a particular temperature. It depends on the wind, the design of the specific model trailer you have, the temperature of the water going into the tank, the length of time it is exposed, and the frequency and/or volume of use.

RV antifreeze will lower the gray tank's freezing point, but its effectiveness is reduced the more it is diluted. Read the bottle and figure out how much you'd need to protect the tank at the lowest temperature of the night.

Some folks, when camping in the winter, leave the trailer winterized and just use bottled water, campground toilets, etc. rather than risk a freeze-up. Maybe this could be an option for you?

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Old 08-21-2004, 03:32 PM   #3
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just run your furnace.

i use mine for deer hunting for 3 days to a week in temps down to the mid teens at night. you will use alot of propane, but it is cheaper than fixing major plumbing problems.

be prepared to winterize at a moments notice, just in case your furnace quits, or you have a power outage, generator failure etc.

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Old 08-21-2004, 09:46 PM   #4
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Originally Posted by luckydc
At what temperature will a holding tank freeze? I know the scienific answer, but need the practical answer for trailers.
Advice is appreciated!
We see the frozen-tank problem daily during ski season up here. Bottom line, however, is that it takes sub-freezing weather consistently for a good number of hours to freeze up a tank, particularly a tank that is nearing full and particularly where daytime temps reach well above freezing. If you're going to be where it drops below freezing only for an hour or two in the early morning, your tanks will probably be just fine. (Not so, however, your water and sewer hoses, which contain less and will freeze more rapidly. Best to disconnect and drain your water hose at night and to use your sewer hose only when you need to dump the rig.)

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Old 08-21-2004, 09:51 PM   #5
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Burr. I hate the thought of anything like that happening.
Just adding my 2 worth

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Old 08-22-2004, 06:26 AM   #6
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In extreme circumstances, you could add rock salt to the holding tank. A 10% addition (10# for 10 gallons) would depress the freezing point to 20 degrees.
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Old 08-28-2004, 03:20 AM   #7
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Thanks all for the advice. Good point on the hoses, Lynn. Hadn't thought of that!


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