Your RV’s built-in black tank flush port was designed to spray water inside the tank and help clean it out.
But with zero visibility into the actual black tank itself, it’s hard to tell how much that spray actually removes, if anything at all.
Ross, from the RV Tips & Travels YouTube channel, performed a test that made the process visible using a real holding tank with a clear lid.
Let’s see what his tests showed!
Testing the rinser on its own
Ross installed a Valterra spray nozzle in a polyethylene black tank, opposite the drain. Working sensors, a vent, and drain plumbing helped recreate an actual RV installation, while water pressure was regulated to 50 PSI.
To prepare the tank, he added water, toilet paper, and a synthetic waste mixture over time to simulate repeated toilet use. He described the mixture as based on a NASA testing recipe, with corn added to the contents.
Once the tank was roughly three-quarters full, he drained it and examined what remained.
Watch the entire testing process below.
So, what did Ross find? At first, dirty liquid, wall residue, and clumps were still visible inside.
The drain stayed open throughout the rinsing tests. That allowed the camera to show what the installed nozzle could accomplish by spraying a recently drained tank, without help from refilling it and dumping again.
Five minutes accomplished more than a quick rinse
After one minute, the nozzle had pushed more liquid toward the outlet and cleaned residue from the three walls its jets reached. Larger pieces remained on the floor, and toilet paper was still attached to a tank sensor.
Four additional minutes produced a noticeable improvement. More dirty water had cleared, part of the middle of the tank was cleaner, and lighter debris had moved closer to the drain. However, two larger wads of paper and waste substitute remained, along with the paper on the sensor.
By ten minutes, almost all the liquid remaining inside had been replaced by clean water. Some areas continued to improve, but heavier clumps resisted the spray.
That was one of the clearest findings: cleaner water and leftover debris existed in the tank at the same time. Through the clear lid, you could see material that the running water had yet to carry out.
Tank treatment left less material behind
For another round, Ross added a dose of Liquified tank treatment. He reported using the same amounts of water, toilet paper, and waste substitute over the same filling period.
After draining, this batch left fewer substantial clumps behind than the treatment-free test.
Checks at one, five, and ten minutes showed a familiar pattern. Dirty liquid cleared fairly easily, the spray cleaned wall residue, and heavier pieces were harder to move. Progress again slowed by the ten-minute mark.
The treatment round also began without toilet paper stuck to the sensors. Since the sensors were already clear, that part of the test offered no evidence of the nozzle removing stuck paper from them.
Related: The Most Popular RV Black Tank Treatments Were Put to the Test. One Came Out on Top
Dried buildup was much harder to remove
The final round tested material that had been allowed to dry. This batch included the synthetic waste mixture, peanut butter, pumpkin pie filling, and corn, which sat in the tank without water for three days.
Ross then ran the rinser for three five-minute intervals.
After 15 minutes, much of the dried material remained. The most noticeable cleaning occurred where a jet directly struck the opposite wall.
Compared with the earlier rounds, the dried deposits made the spray much less effective.
The takeaway is that the rinser is better suited to regular cleaning while residue is wet than occasional attempts to remove established buildup.
Why the test left out refilling and dumping again
Several viewers described using refill-and-dump cycles as part of their own cleaning routines. Essentially, filling the tank back up with water and dumping again, which tests show as one of the most effective ways to clean a black tank. Their comments prompted Ross to explain the demonstration’s purpose.
In a pinned comment beneath the video, he clarified that he wanted to establish how well the rinser performed on its own before comparing additional cleaning steps.
He expected refilling and dumping again would remove more material, but reserved that comparison for another test. This video therefore shows the nozzle’s capabilities, not evidence that one complete cleaning routine outperforms another.
What the results tell RV owners
Five minutes of rinsing left this tank noticeably cleaner than one minute. After ten minutes, though, larger clumps were still sitting on the floor, even with mostly clean water around them. Leaving the rinser running longer was helping less as time went on.
My recommendation is to refill the black tank by dumping water from a 5-gallon bucket down the toilet and dump it a couple of times. If you already have a built-in rinser, you could also use it to help wash down the walls if you wish. But if your RV doesn’t have one, I wouldn’t spend the time and money installing one just for this.
Note: Your setup may give different results, since the tank’s shape, nozzle, and water pressure all affect where the spray reaches and what it can move.
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