One of the oldest RV black tank cleaning tricks is surprisingly simple: dump a bag of ice down the toilet, add some water, and go for a drive.
The theory is that the ice cubes slide around inside the tank, scrubbing waste from the walls and knocking buildup off the tank sensors. RVers still recommend the method today, and the advice has appeared in RV publications for years.
An archived MotorHome Magazine Q&A, for example, recommended adding about 10 gallons of fresh water and 20 pounds of ice before driving on winding roads to help the ice scrub the inside of the tank.
It sounds reasonable. But tests that let us actually see what happens inside the tank tell a different story.
The ice barely moved during one well-known test
James from The Fit RV put the ice trick to the test using a clear black tank simulator.
He added simulated waste based on research from NASA scientists, along with toilet paper and material stuck to the sides of the tank. The tank was then left in the hot sun before being loaded into the back of a truck.
Two cameras recorded what happened while he drove for roughly an hour, including one camera looking directly inside the tank.
The results were not very impressive.
Some material was removed where the ice and water reached it, but a large deposit remained. More surprisingly, the ice spent much of the drive barely moving.
James drove far more aggressively than someone normally would with an RV and still struggled to get the ice very far up the tank walls.
There was another problem. Adding more ice didn’t necessarily create more cleaning power. Too much ice could pack together and stop moving. Add too much water and the cubes started floating instead of sliding along the bottom.
His test showed that ice can produce some limited cleaning action, but most of it was confined to the area the ice and water could actually reach.
Ice isn’t much of a scrubber
The problem becomes easier to understand when you look at how ice behaves inside a wet plastic tank.
Ice sliding across a wet surface creates very little friction. When a cube encounters something firmly stuck to the tank, it can simply change direction rather than scrape the material away.
That’s exactly what the cameras in The Fit RV test showed. Even during hard turns and stops, the cubes tended to slide and shift rather than scour the tank.
James ultimately concluded that the cleaning he observed was only marginally better than what he would expect from water alone.
He later revisited the subject in his black tank maintenance tips and said his experiment convinced him that filling the tank with water could produce essentially the same result without buying bags of ice.
Another test reached a similar result
Unique Camping + Marine has also tested the ice method and says it found very little meaningful abrasion against the tank walls.
According to the company, much of the ice floated or moved around near the middle of the tank rather than scraping its sides.
Unique sells black tank cleaning products, so its recommendation to use a waste-digesting cleaner comes with an obvious commercial interest. Still, its description of what the ice actually does inside the tank closely matches what can be seen in The Fit RV’s clear-tank experiment.
Unique also offers an interesting explanation for why some RVers remain convinced the trick works: ice eventually becomes water.
Adding water, letting the tank soak, and driving around can all help loosen material. An RVer who does those things while using ice may see an improvement and give the cubes credit for cleaning the tank.
Unique also suggests ice could temporarily cool a hot tank and help with odors on very hot days, although its video does not provide measurements showing how large or long-lasting that effect might be.
So what works better than ice?
Water may be more useful when it is moving forcefully rather than frozen into cubes.
We recently covered another black tank test using a real RV holding tank with a clear top. In that experiment, Ross from RV Tips & Travels found that rapidly pouring about five gallons of water through the toilet created enough turbulence to move material that remained after two complete refill-and-dump cycles.
It was only one test, and tank layouts vary, but the results support the same basic lesson seen in the ice experiment: moving water can do much of the work RVers sometimes credit to ice.
For stubborn buildup, soaking also gives water more time to soften material instead of relying on ice to physically scrape it away.
That approach shows up in manufacturer cleaning instructions too. Thetford’s instructions for cleaning fouled holding-tank sensors call for filling the tank, driving to mix the contents, allowing it to sit for 24 hours, driving again, and then dumping and rinsing.
Should you stop putting ice in your black tank?
Little evidence shows that dumping ice into a black tank provides the aggressive scrubbing action commonly associated with the trick.
The Fit RV’s test did show a small amount of cleaning, so calling the method completely useless would go too far. The bigger issue is that much of the benefit appears to come from the water and soaking rather than the ice itself.
If you have leftover ice at the end of a camping trip, putting it down the toilet probably won’t hurt anything. Even The Fit RV has said as much.
Buying bags of ice specifically to scrub a dirty black tank is harder to justify. Based on what these tests show, filling, soaking, and properly rinsing the tank will likely do just as much without relying on ice cubes to do a job they aren’t particularly good at.
Write a comment