Today, we’re covering the most debated topic in RV black tank management: should you liquefy solid waste or not? Which method works best to get as much stuff out of these tanks and keep them as reasonably clean as possible? Today, we’re going to find out.
When it comes to RV tank treatments, there are a lot of different options. There are manufactured products, homemade recipes, and many different opinions on what to do and what not to do. Among all of this information, we only have a few pieces of the puzzle. We know what’s going into the tank, and we can see, on a limited basis, what’s coming out of the tank. But we don’t know what’s happening inside the tank as it’s being dumped. And probably the most important thing is that we don’t see what’s left in the tank after it’s been dumped.
So here’s what we’ll do: I’ll use two identical 32-gallon storage bins. These are made out of polyethene, the same material used for RV black tanks, so there should be no variation. I sealed everything up—it’s not pretty, but it will withstand 30 gallons of water pressure. I’ve positioned the tanks at a slight angle down towards the drain to mimic the angle at which most black tank bottoms are designed. I even installed vents on the lids so the tank contents breathe the same way they would in an RV, and I’ve gotten the all-clear from my septic service company that I can dump into this pipe here.
This test today is because there are two schools of thought. The first argument is that it will not fully exit the tank if you don’t break down solid waste. The idea is that solids need liquids to be pushed or pulled out of the tank. As the tank empties, the water pressure pulling everything out decreases. As the water level lowers, the solids still in the tank begin to contact the bottom of the tank, creating friction. Both factors combined mean you’ll still have solids remaining in the tank. The idea that all the solids don’t fully exit the tank is not a myth.
However, this leads to the second argument: Liquidifying solid waste is unnecessary if you add a surfactant solution. When added to water, a surfactant reduces the surface tension among all the different items in the tank. In simpler terms, a surfactant makes everything inside the tank slippery, so everything slides out nice and easy, even as the water pressure decreases and the friction increases.
Okay, let’s start the test. First, every time we dump a black tank, we’re putting water back into it. Anywhere from 5 to 10% capacity is good. We’re using 32-gallon totes, so let’s add 3 gallons of water to each tank. Next, we want to add our treatments. One ounce of liquefied will treat up to 40 gallons. The other tank is going to get the surfactant mixture. You start with a clean and empty 1-gallon jug to make the solution. Add 40 oz of pine sol. The next ingredient is 8 oz of Calgon bath pearls. Then, mix the rest of the jug with water, cap the jug, and shake to mix everything. Now that our solution is complete, we will add, Per the recommendation on CleanTank’s website, 4 oz is enough to treat the tank. They say you can add up to 8 oz if it’s extremely hot outside, but it’s not hot—about 70° here. They also say to add 8 oz if it will take considerable time to fill the tank. That’s not going to be the case in today’s test. We’re going to have this tank filled in about 2 days.
I’m sure many of you have seen dog food used in black tank videos. While dog food may be good to see if a tank treatment will break down solids, there’s a problem with dog food in our test today: the size of dog food does not accurately represent what would normally be in a black tank. I will still use dog food to describe some of the smaller stuff in the black tank, but we will also use peeled bananas. Remember, this is not a test to determine if our tank treatments break down solid waste. Today, we’re comparing how solids exit the tank versus how liquefied solids exit the tank. To get the best and most accurate results, we need solids in our test tank to accurately represent the size, shape, weight, and consistency of what would normally be in a black tank. I think bananas are an extremely accurate representation of those features.
I will add dog food, bananas, septic-safe toilet paper, and water to each tank equally. Instead of doing this all at once, I will do this occasionally over the next 2 days. In the interest of filling these tanks as they would be filled in real life, I’ll be adding to the tanks based on normal bathroom usage for about three people and plenty of water being used while flushing. I’ll reevaluate when our tanks are about 80% full, which would be the ideal time to dump them.
While filling up the tanks, let’s talk about the actual costs. So far, the Pine-Sol was $7.58 for 40 oz, and we used all 40 oz for the mixture. The Calgon beads were $15 for 16 oz. You’ll only need 8 oz for the final mix, so your final cost is $7.50. The total cost for our surfactant solution is $15.88, not counting the cost of the jug, which I’m assuming most people will just repurpose, and the cost of a gallon of tap water, which is insignificant. There are 128 oz in a gallon. The recommended dosage is 4 oz, so you’ll get 32 applications out of 1 gallon, or 47 cents per 4 oz application. If you double the solution up to 8 oz, it’ll double your cost. A 32 oz bottle of Liquefied is $25, so each treatment is 1 oz. That works out to about 78 cents per application. So, based on the prices that I paid—and again, that may change depending on where you get your ingredients—the surfactant solution is about 31 cents less per application. But with Liquefied, you get the bottle you need, and it also comes with a built-in measuring applicator.
Two changes have been made to our setup. Neither will affect our test, but I think full disclosure is important in experiments like this. I added a couple of tubes between the tanks and the plywood to evenly distribute the weight’s stress over the plywood, but both tanks are still at the same angle. I also added bricks to hold the covers because we’ve been having windy days, and I wanted more support than the plastic latches.
This is the tank with the liquefied toilet treatment. It did exactly as expected: it broke most of the solids down. It seems to have not liquefied all the bananas, at least the ones most recently added, I’m assuming. But that’s okay; we have a very full tank of liquefied solids, which is what we want for our test. By the way, each tank got eight bananas over the 3 and 1/2 days. Three were added whole, and the rest were cut up. Whatever I did in one tank, I did in the other tank. The same goes for the dog food, the water, and even the toilet paper, which was equal to the sheet. And I know these tanks look super full, but I used water each time I added to the tanks. Even with all this floating on the top, it’s all water underneath the tank. It’s probably at least 90% water.
Moving over to the surfactant tank, I thought this would be the case. Nothing is broken down as expected. The dog food is saturated. We’ve all seen what happens when dog food gets bumped over into the water bowl, so nothing unexpected here. So, we’re going to dump the liquefied tank first. This is when the drain is under extreme pressure. Once this water level drops below the pipe, the pressure will drastically decrease, and at that point, it will take much longer for the remainder of The tank to drain out, so while the liquefied tank is draining, let’s drain the surfactant tank. We’re going to see the same thing. The pressure and movement will slow down once the tank level drops past the pipe. Here is what is most interesting to me so far in this test: solids stop moving towards the drain and out of the tank long before the water level even reaches the bottom of the drain pipe and long before they even make contact with the bottom. If solids are on the other side of the tank, which they will be, there’s never enough force during the entire dumping process to move solids over to the drain and out of the tank. This is very interesting. After a few minutes, the rate at which the water exits is so slow that it’s not moving anything out of the tank.
Okay, let me pause this for a second and talk about something. Both tanks have stuff left in the bottom. Forget the two treatments we’re comparing for a minute, and let’s go back to what I said earlier in the video. The idea is that solids need liquids to be pushed or pulled out of the tank. This is, without a doubt, confirmed. Solids absolutely need liquid to be moved out of the tank, and as the water level lowers, the pressure decreases, and things just get left behind in the tank. So, at this point, we have many solids left in the surfactant tank. Any solids in the liquefied tank that haven’t had a chance to break down fully are also left in the tank. I think this is the most important thing we’ve seen so far in this video. Solids stop moving towards the drain pipe and out of the tank long before the water level gets to the bottom and completely drained. So, from my test, the surfactant solution does not work to make everything slippery, you know, so it slides out of the tank. Liquefying waste also doesn’t get everything out, but it gets more out than not liquefying waste.
The next step in today’s test will be very eye-opening to, I think, many people who haven’t rinsed their tanks before. But before we get to that, we must discuss a few things. An argument I’ve heard before making this video was that liquefying solid waste turns some of the contents of your black tank into a pasty material, and I will agree. The argument goes on to say that you should not liquefy waste because these are not septic tanks but holding tanks. We are liquefying solid waste to get it out of the tank. We’ve seen in the video that all solids do not exit the tank on the first dump. I think an argument to the argument would be that if we don’t liquefy waste, we’re left with a bunch of solid waste in the tank because the surfactant solution did not help move anything out. We’ll come back to this argument after we rinse the tanks because that’s when we’ll know if the paste in the tank is more of a problem than the alternative, which is having solids in the tank.
So, the next thing I want to talk about is that Clean Tank recommends adding 4 to 8 ounces of surfactant solution to the tank after you dump it. I know the question is coming, so I’ll address it now: why did I choose to use 4 oz instead of 8 oz, 6 oz or 7 oz, whatever? First, I wanted to be fair. I wanted to compare the minimum recommended dosage of Liquefied, 1 oz, to the minimum recommended dosage of the surfactant solution, 4 oz. Second, Clean Tank states that this surfactant solution will work best in a tank that has been recently hydro-jetted, which is a cleaning service they provide. These tanks are brand new; they’ve never been used, so they are perfectly clean. Third, these bins will hold 32 gallons. Now, some micro campers have black tanks smaller than 32 gallons. Still, once you start getting into your 20 to 25-foot travel trailers and larger ones, you’ll start seeing black tanks averaging around 35 to 40 gallons, and they even go up to 50 or 60 gallons, depending on the size of your RV. For all of those reasons, I chose 4 ounces. We’re comparing the minimum recommended dosages. We’re using brand-new clean tanks, which are on the smaller side. If 4 oz is even mentioned, I can’t imagine better conditions for that minimum recommended amount.
The last thing I want to cover before we do the rinse is why I decided to put the flame on the corner of the bin, and the simple answer is that’s where it fits best on the bins that I got. But it doesn’t matter because black tank drain pipes are positioned everywhere, depending on your RV. Now, the bottoms of these bins have rounded edges, so I could not put the tip of the drain pipe at the bottom of the tank. The pipe is about 6 inches from the bottom. If the drain pipes were located at the bottom of the tank, we would still not get any significant amount of additional solids out of the tank because when the water level reaches the middle of the drain pipe, the water pressure has dropped so much at that point that the only solids exiting the tank are the ones near the pipe. I was very surprised to see this, and I think it’s happening for three reasons. The solids throughout the tank are touching each other; they have surface tension against each other, essentially creating a larger mass of solids, which is more difficult to move. There’s also friction of the solids against the sides and, eventually, the bottom of the tank. Third, gravity pulls the solids straight down. All of those factors combined overcome the ability of the low water pressure at that point to move solids out. Having the drain pipe a little bit higher than the bottom of the tank creates a buffer between the bottom of the tank and the solids, which also reduces friction, and it may allow more solids to exit our test tanks than what we would see in real life with the drain pipe at the bottom of the tank.
Of course, yes, we’ll get a little more water out over time, but again, solids are done moving long before the water level reaches the bottom of the drain, regardless of location. I think there’s this huge misconception that once you drain a waste tank, everything inside that tank immediately flies down and out of that 3-inch pipe. I know that’s what I would picture in my head, but that’s not what happens in real life. The reality is that once the water level reaches the drain pipe, no matter where it’s located, everything pretty much stops moving except for liquids.
So we’re going to backfill and rinse the tanks now. I think you’re going to be very surprised. I’m connecting a water source to the Rhino Blaster flush inlet. I have a vacuum breaker at the end of the hose with the drain valve closed. I’m turning on the water and starting to backfill the tank. I’m only going to fill it so the water level is slightly above the drain pipe, and this is what it looks like in the tank as the water is being pumped in. Then, I will turn off the water and immediately dump the tank. Now, this is what I’m talking about. Now, we are getting somewhere. We got a lot out of what was left in the tank after just one rinse, and we didn’t even have to fill the entire tank. I’m going to do the same thing on the liquefied tank. I’ll fill it up about 20 to 25% so it’s past the drain valve, turn off the water, and immediately dump it.
So this is interesting. The paste is gone. The tank is noticeably cleaner after one rinse. If you use more water to backfill these tanks than I did in this video, they’ll probably even come out cleaner, or you can simply rinse them a second or third time. But we still have a test to complete, so let’s compare our tanks after one rinse. There are still some solids in the surfactant tank; there are no solids or paste in the liquefied tank. Now, you can dump 25 times if you want, and eventually, your tanks will be as clean as they’re ever realistically going to be. But after one low-volume rinse on both tanks, I choose to use a tank treatment that liquefies waste over a surfactant solution that does nothing to help move solids out of the tank.
Ladies and gentlemen, liquids move better than solids, and flushing is the key. I hope you guys learned something today. I know that I did.