--- title: "An RVer Tested Two Popular Black Tank Cleaning Methods. One Clearly Worked Better" url: "https://camperfaqs.com/two-popular-black-tank-cleaning-methods-tested" author: "Tory Jon" published: "2026-09-21T13:09:26-05:00" modified: "2026-09-21T13:10:19-05:00" --- # An RVer Tested Two Popular Black Tank Cleaning Methods. One Clearly Worked Better RVers have come up with plenty of ways to clean a black tank after dumping. One popular method is to refill the tank with fresh water and dump it again. Another is much simpler: pour several gallons of water straight down the toilet. Ross from [RV Tips & Travels](https://www.youtube.com/@RVTIPSANDTRAVELS) put those two methods head-to-head using a real RV black tank with a clear top. The difference between them was much larger than he expected. [Watch this video on YouTube](https://www.youtube.com/watch?v=qYh7Hf2CR10) *Ross from RV Tips & Travels compares two common black tank cleaning methods using a real RV holding tank.* ## A Real Black Tank Made the Test Possible Ross built his test rig around an actual polyethylene RV holding tank rather than a clear plastic container. Before choosing it, he researched 92 black tanks used by RV manufacturers and calculated average capacities and dimensions. His numbers put the average tank at roughly 40 gallons. The test tank was outfitted much like one installed in an RV, with a gate valve, termination plumbing, vent, tank sensors, and a pipe representing the toilet. The top was replaced with clear plexiglass so he could see exactly what remained after each dump. Instead of actual waste, Ross used a synthetic mixture designed to behave similarly in water. He gradually added the mixture, toilet paper, and water over several days to better simulate how a family would actually use the tank. ## The First Dump Left More Behind Than You Might Think Opening the gate valve sent most of the tank's contents rushing out, but the clear top showed what RVers normally cannot see. Residue remained on the walls. Toilet paper and heavier material were still scattered across the bottom, and some liquid remained in low areas of the tank. Ross explained that flow slows as the water level drops. RV holding tanks can also flex under the weight of their contents, which can create areas where liquid and debris remain after the main rush of water is gone. > **Clear water coming through the sewer hose does not necessarily mean the black tank is actually empty.** That set up the real question: What is the better way to remove the material left behind? ## First Up: Backfill the Tank and Dump It Again For the first method, Ross used external backfilling devices including a Camco Rhino Blaster and Valterra Flush King. These attach near the sewer outlet and allow fresh water to travel backward through the plumbing after the initial dump. With the RV's gate valve open and the valve on the backfill device closed, water eventually fills the black tank again. The idea is to restore a large volume of water so another dump creates enough flow to carry out whatever remained. Ross filled the tank back to roughly the same level as before the original dump and opened the valve again. The result surprised him. Some toilet paper and other floating material moved, but much of the heavier debris on the bottom barely changed. He refilled the tank and dumped it a second time, with similar results. Backfilling clearly did something. It was particularly effective at lifting toilet paper into the water so it had another chance to leave the tank. What it struggled to do was move heavier material that stayed on the floor. ## Then Came the 5-Gallon Bucket Instead of refilling the entire tank a third time, Ross left the drain valve open and rapidly poured roughly five gallons of water through the toilet opening. That changed things immediately. The falling water hit the tank with enough force to create considerable turbulence, stirring up material that had remained largely untouched during the previous two backfills. After just one bucket, the improvement was noticeably greater than what Ross had seen after two complete refill-and-dump cycles. A second bucket removed even more. > **One 5-gallon bucket produced a bigger visible change than two full backfills in this test.** Ross ultimately gave the bucket method the win, noting that it also used considerably less water and took less time. ## Why Did the Bucket Work Better? The test suggests the amount of water may matter less than how that water moves through the tank. Backfilling gradually raises the water level across the entire tank. Material that floats can rise with it and get another chance to leave when the valve opens. Heavy debris sitting on the bottom may not move much at all. Dumping five gallons quickly through the toilet creates a concentrated rush of water. That turbulence can knock material loose, lift it from the floor, and push it into the stream already moving toward the drain. Ross came away from the experiment believing direct water pressure and agitation were more effective at moving stubborn material than simply filling the tank and relying on gravity to drain it again. ## Tank Treatment Helped, But the Pattern Stayed the Same Ross repeated the process after adding a black tank treatment designed to break down solid waste. The treated tank was noticeably cleaner after the initial dump than the untreated one. Still, backfilling behaved much the same way. Toilet paper and other floating material moved more easily, while heavier material remained harder to dislodge. The bucket dumps again produced more visible agitation inside the tank. That makes treatment and rinsing two separate parts of the process. Breaking material down before dumping can make it easier to remove, but water movement still appears to play a major role in what actually leaves the tank. ## A Few Things to Keep in Mind This was a useful test, but it doesn't prove that a bucket will outperform every flushing method on every RV. - **The bucket came after two backfills.** Ross did not perform the bucket test immediately after the initial dump. He acknowledged that the previous cycles could have affected the result and plans to test the bucket first in another experiment. - **RV plumbing varies.** Some rigs have straighter termination plumbing that may allow an external rinser to direct more water toward the tank. - **Tank and toilet placement matter.** The location of the toilet opening, drain, and internal plumbing can change how water moves across the tank. - **The test tank already slopes toward the drain.** Ross later noted that his own trailer's tank is flatter, so some RV tanks may drain even less effectively. - **This wasn't a test of every rinsing system.** Built-in tank sprayers, toilet wands, and garden hoses placed through the toilet create different water patterns and could perform differently. Ross has already said more tests are coming, including methods that apply water pressure directly inside the tank. ## The Bigger Lesson May Be Turbulence The most interesting result isn't necessarily that every RVer should start carrying a 5-gallon bucket. It's what the transparent tank revealed about the cleaning process. Two complete backfills used far more water and took considerably longer, yet much of the heavier material remained on the bottom. A relatively small amount of water delivered quickly through the toilet created enough turbulence to move material that the previous drains had left behind. For a part of the RV that owners normally never see inside, that was a pretty revealing five gallons of water.