Saturday, June 3, 2023


Our RV holding tank is frozen – Help!

gary-736Dear Gary,
How do I unfreeze a black holding tank on my RV? I’m not sure if it’s full or not. The dump valve is frozen shut also. I only need options for a stationary RV as I can’t get the 5th wheel to a shop. Emergency! Help! —Mike A.

Dear Mike,

Sorry to hear about your holding tank issues; so exasperating, I know! If you’re careful, you can use a hair dryer or heat gun to help thaw the tank. Don’t stay in one focused area for any length of time. ABS and polyethylene tanks can be melted quite quickly if the heat is too hot or you linger too long in one spot. Start at the uppermost level of the tank and work your way down all exposed sides of the tank until you reach the termination valve. Keep the gun in motion at all times. Repeat as necessary until you can open the termination valve and you hear contents evacuating.

Once evacuated, flushed and the valve closed, add a gallon or two of RV antifreeze or even windshield washer fluid to the tank through the toilet. Be sure the strength is applicable for the expected temperatures, though. And be sure it is RV antifreeze and that the windshield fluid is permitted to be dumped into your septic system. If possible, see if you can add insulation around all sides of the holding tank. In sub-freezing temps, it is difficult, but doable in most cases to continue to use the on-board waste systems.

Unfortunately, the only other alternative I can think of contain the words “wait,” “spring” and “thaw” in it. If you have enclosed holding tanks, you can place a 100-watt trouble light inside the compartment to help keep it warm after you finally get it evacuated completely. Also consider purchasing an aftermarket holding tank heating pad prior to, say, next September.

Read more from Gary Bunzer at the See Gary’s videos about RV repair and maintenance.




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Bryan Pennington
5 years ago

I had the bad experience of having to use my travel trailer in freezing weather once and the flush valve (termination valve) froze.
I laid under the trailer with my wife’s hair dryer freezing my butt off thawing the valve. After it thawed I added a temporary layer of insulation until I could resolve the situation permanently.
Remember that ice crystals form at the lowest point float up to the top and if supported by 32degree will form an ice sheet at the top. Chances are that the top of the tank or upper water level will not freeze, but, the valve, the lowest level of the tank will. Once the valve is thawed the warmer waste as it empties should eliminate any remaining ice that may have formed.

5 years ago

Salt is safe to use in a waste tank. Make a saturated solution of common table salt and water and pour it down the toilet. The finer table salt works faster than rock salt.

5 years ago

My ‘go-to’ place had a solution for this for me. I have a Coachmen class ‘A’ with enclosed tanks so no tank heaters for me. He installed a nautical solution, a Bilge Heater in my Sanitary bay that is thermostatically controlled. It has a fan that distributes the heat…solved the problem.

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