Holding Tank Treatments

This post was written by Lee who as you can see is extremely passionate about tank management. 

This is a followup to my post a few days ago about not leaving your gray tank open when hooked up to a sewer connection.  Today I am going to save you money and time talking about “treatments” for your tanks. Before I begin, let me say that what follows is my opinion (except science, which isn’t an opinion) and your mileage may vary. If you have a way you do things, and don’t want to change, by all means, keep doing what you’re doing! I am not interested in changing hearts and minds. If you’ve been RVing for a while then you already know this, and if you’re new then this will hopefully be useful and helpful information.

This is probably going to be a very unpopular opinion based on that fact that I’ve certainly been treated to lots of very strong feelings about this topic. Some of which defy all logic, learning and attempts to prove them! Here’s what my Mom would have referred to as the “Reader’s Digest” version for those who want to cut to the chase: There is no product  that you can add to your tanks that will do anything at all to reduce or eliminate odors or reduce or eliminate poo or paper.

For those interested in the longer format, read on!

There’s nothing you can add to the tank that will do anything because, really, science just does’t work that way. Except in a very few rare cases, or in very large quantities, anything you buy and put in either your black or gray tank is a waste of time and money. You are literally flushing money down the drain.


The number one clue that this is the case is that all of the methods and products are sold for use in both black and gray tanks to “break down” solids, control odors, and “lubricate” valves.  Take a moment to think about that. The contents of black and gray tanks are not even remotely the same, so the idea that a few ounces of anything will do all of those things is absurd. The first thing to consider is that whatever you are putting in there is going to be seriously diluted. Let’s take a look at some examples, do some math, and compare the claims to reality! Science is fun! Sorry he gets like this sometimes.  It’s generally worth hearing him out though. – Trace



Right off the bat, I am going to debunk the much beloved GEO method.  This is essentially using Calgon, water, bleach, and laundry detergent to clean your tank – Trace.   Since the mid 80’s people have been swearing by this method, which was apparently “invented” by someone who uses their RV “at least one weekend” per month, and based on that says that his RV bathroom gets “heavy use”. You haven’t seen “heavy use” of an RV toilet until you live in an RV full time and are prepping for a colonoscopy- Trace.

The method claims that you can keep your tank clean and control odors. Nonsense. There is no such thing as a clean black tank which has ever been used. It describes the result as a tank that is “clean, sanitized and disinfected”. I think that’s a pretty wildly irresponsible claim. I personally guarantee you that there is no way pouring anything down a toilet will result in the tank being “sanitized and disinfected”. I am willing to bet that the guy who invented the GEO method would be unwilling to drink clean water run through his own “sanitized and disinfected” tank.

Anyways, here’s how you are supposed to invoke this sorcery. First, you empty your tanks. Then dissolve 2 cups of Calgon water softener into a gallon of warm water and pour it down the toilet. Pour 1 cup of laundry detergent (or dish soap) down the toilet to clean the tank. Then you are also supposed to add half a gallon of bleach when the tank is about half full to “deodorize, sanitize and disinfect them”. There is no mention of adjusting these quantities for the size of the tank. Apparently this magical elixir is able to adjust it’s properties to fit the tank size!

Which brings me to the theory where you can adjust the ingredients and the amounts and still get the same result. That’s ridiculous. Imagine changing a cake recipe by tripling the amount of flour, adding 4 cups of vodka, and 14 eggs, and expecting to get anything resembling a cake at the end. The fact that the ingredients and quantities vary is a pretty good indicator that this is made-up nonsense. But even if you pick one “official” list of ingredients and quantities, then you will still get the same result; a black tank full of poo and pee and paper with trace amounts of soap, salt and bleach. Calgon is nothing more than water softener.  It’s active ingredient has no beneficial chemical reaction with anything that is likely to be found in black or gray water. In addition, that level of dilution (two cups in 50 gallons) renders it nearly inert.

The theory behind using it is that the water softener makes the inside of the tank slippery so things won’t stick to it. Utter garbage. In order for that to be the case you would need to coat the interior of the tank. Pouring a gallon of solution into it just isn’t going to do that. Instead you will have a gallon of solution in the tank and when you add other things to the tank, it’s just going to mix together and dilute.

The next ingredient in the GEO method is 1 cup of soap. Laundry or dish soap. Again, what does it tell you that you can use either of those things? How about shampoo? Dog shampoo? Dry shampoo? Dandruff shampoo for sensitive skin? An equivalent amount of soap shavings from a bar of soap?

It is possible that the soap will help in breaking up grease in a gray tank, but that’s really only if there is agitation.  If you’re not in motion, that’s not going to happen.  Furthermore, almost all manufacturers of all soap recommend a 1% solution for best results.  For a 50 gallon tank this would be a half gallon, or 8 cups. Using just 1 cup is going to be a severely diluted solution. The next time you wash dishes, try doing it with just a few drops of soap and see what results you get.

I don’t even know what to say about the bleach. , apart from most people think of bleach as “strong stuff” so maybe it’s just in there to make us think we’re really bringing out the “big guns”. I’m not saying to be reckless with bleach, it can be dangerous, but again, science is here to help. To use bleach as a disinfectant, you need one cup per gallon. So again, a 50 gallon tank would need 50 cups, or just over 3 gallons.  And of course, all of these ingredients are only active for a very short time. Most black tanks get filled about every 10 days, and these ingredients would be inert within 3-5 days.

I would also like to point out that there is nothing in the GEO method that “lubricates”. I’ve heard people say that the soap does the trick, but when was the last time you heard of someone recommending using soap as a lubricant? I don’t want to get too personal here but there is a reason smart people don’t use soap as a sexual lubricant.  If you ever tried you know it is not very effective. – Trace

Soap breaks up oil, it’s not a substitute for it. Dish detergent might make a finger slippery for a few minutes to get a tight ring off, but it’s not a method to lubricate a mechanical device such as a gate valve. And if you think that any of this stuff makes the inside of the tank itself more slippery, and allows more stuff to drain out, that’s not how fluid dynamics works. In order for that to work, you would need to coat the inside of the tank just like greasing a cake pan before using it. The lubricant wills only going to work where it is applied to the material, and that material would have to be clean and dry.

The inside of your tanks have not been clean or dry since the first time you used them. Also, the tank is made of a plastic that’s pretty well hydrophobic, so not much sticks to it. Mostly what’s in a tank that smells bad isn’t sticking so much as floating or sitting under the water, and most of it goes away when you empty the tank.


But what about all of the other products available that are specifically formulated to do all these things, using “chemistry”  to somehow magically convert solid and liquid human waste and paper in the case of black tanks, and oil, hair and food particles in the case of a gray tanks?


Every product available commercially is made up of more or less the same stuff. It’s all varieties of soaps and salts and perfumes. None of it can work magic. There is no science that supports the claims they make, and the same principles of what I described with the GEO method go for other chemicals and substances. Just because a word is hard to pronounce, or we don’t know what it means, doesn’t mean it isn’t bound by the laws of physics and chemistry.

There are very few things that can actually be used to treat black water, but they require time to work and a balance of bacteria, enzymes, solids and water that is carefully maintained, and none of that is going to happen in a tank that is emptied every 7-10 days. Porta-potty companies used to use formaldehyde, but that’s more or less illegal in every state now. Neutralizers and scents used in porta-potties do and will work, but are pretty expensive, and those tanks are emptied a lot more often than people think.

Also, their primary tactic is volume as truly staggering amounts of biocides and perfumes are used in portapotties. You’ll need a second vehicle and some wealth to be able to afford it and transport it. Also, here’s a fun fact, the blue dye serves no purpose other than to mask the appearance of what it mixes with. I would like to interject here that we spent three summers cleaning bathrooms and we got up close and personal with pit toilets and port-a-johns.  Since the company we worked for was trying to control costs we were limited on the amount of solutions we were allowed to use.  Essentially based on that experience the toilets would smell clean for roughly 24 hours after pumping (less if it was a hot day) and nothing we tried lasted longer than a couple of days.  You know what sort of worked?  Air fresheners. – Trace

So, having told you all about how none of the stuff you can buy will “treat” your tanks, what are you left with? Well, my answer is: nothing. ? If you are using the tanks properly, and managing them the way they were designed to be managed, then they should operate as designed, which means minimal odors and chances of clogging. If you experiencing either odors or clogs, then you are operating the equipment incorrectly, or something is wrong with the equipment.

A holding tank is just that. It “holds” the stuff until you can dump it in a sewer.  It’s just a giant bedpan with some fancy features to make it less gross. Some people think when they’re hooked up they can leave the black tank open to drain directly to the sewer. Don’t do that. If you leave the black tank open to drain directly into the sewer, the liquids will run out and the solids will not and eventually you will end up with a pyramid that is rock hard like concrete. Likewise, you should use plenty of water when you flush, just like at home. If you are stingy with the water, which some people do to maximize how long they can boondock without dumping, then you are upsetting the design balance.

Using special toilet paper is not the solution using more water is. I’ve also heard people talk about only using their black tank for poo, and peeing elsewhere and/or putting toilet paper in a trash can or bag. Again, not having enough liquids in the tank will make it more likely to clog. Paper in and of itself is not a clogging problem.  It will fall apart if any pressure is put on it at all. Clogging is caused by solids, not water or paper, and making sure you have plenty of water in the bowl is the solution.

ANYTHING else that goes into the black tank is going to be a problem. Anything but toilet paper will clog it. Paper towels, wipes, whatever. If it’s not pee, poo or toilet paper, don’t flush it. The brand or type of toilet paper doesn’t matter. All that “swirl it in a glass of water” nonsense is a waste of time. Your RV tank is not a septic system, it doesn’t need septic safe toilet paper. Any toilet paper is OK if you use a bowl of water when you flush and you dump the tank when it’s full instead of only partially full.

And finally, the one thing you can do that will actually be worth the time and effort is to rinse the tank. And by rinse, I mean rinse it out by filling it with water and then emptying it. Dump it, then fill it and dump it again. When you dump the tank, most of the stuff in it will come out, but there will be some that is left behind.  That’s the nature of solids and fluids and gravity.  If you repeat the dumping and filling process, more stuff will come out every time.   You don’t have to do that every time you dump, but once every four or five dumps  will help prevent a buildup of sludge. And whenever possible, drive with the blank tank at least 1/3 to 1/2 full. The acceleration and deceleration of driving will slosh the liquids and solids around break up a lot of the solids, and much more will get cleaned out when you arrive and dump.

Speaking of which, don’t bother pouring ice down the toilet. It will melt long before you get any scrubbing benefit. This is another myth that persists even in the fact of basic science.

Hopefully this was useful information, and you will save yourself some money you can use for more fun stuff. If you have any questions please don’t hesitate to ask them!

UPDATE: I got a question that I was originally going to do a full post on once we started traveling again, but I decided to just go ahead and answer it here and I will update it again with pictures once we start traveling again. 

A reader (hi Jami!) asked about the heavy particles (sediment) that sit on the bottom of the gray tank, and how they can thicken as time goes by. They use a hose to “blast” down the toilet to break up stuff in the black tank, but you can’t really do that with a sink, and even if you could, the “P” traps and other turns would essentially negate the force of the water by the time it got to the gray tank. In particular the reader was concerned about staying put for a longish period of time, and how much sediment they might be building up by not being able to “scrub” the tanks by driving with them 2/3-ish full.

This is an excellent question, and one that I myself pondered about a year ago because we were sitting still for a long time ourselves. I noticed that we did very little actual travelling, and we were basically going from a 4 month stint of gate guarding to a 5 month stint at a summer gig, and not doing a lot of traveling. So I started thinking about how I could solve this problem before it became a problem, because filling up the gray tank and emptying in the same way as rinsing the black tank would tank a lot longer, because it’s a much bigger tank. So, last Spring I decided to try an experiment. We use a Flush King at the very end of the line on the rig, instead of just a black cap, for a variety of reasons. (Don’t let the apparent size of it worry you, the entire valve assembly rotates around the bayonet fittings, so it can be adjusted a full 360°!)


Reason #1, it’s clear plastic, so when I am dumping tanks, I can see what’s happening. It really is good to have an idea of what’s coming out of your tanks and going down the sewer line. If you can’t see, you don’t know. This allows me to monitor how fast things are moving and what’s moving. When I rinse the black tank, I know we’re as clean as we can get when I fill it up and all I see is clear when I dump it.

Reason #2, when I take off the cap, there is nothing in the cap. NOTHING. Because there’s a valve there, anything left in the pipe that might drip down, especially when I lift the front end to hook up, stays behind that gate where it belong, until I hook up a line and open the gate. I never get so much as moisture on my hands.

Reason #3, if there’s a leak in either of my valves, I’m going to know because that clear part is going to have something in it. No surprises!

Reason #4, twice in all of our time doing this, we have had “clogs” in the process of emptying the black tank, in both cases, it was a result of sitting in one place for too long boonndocking and trying to make the tanks last longer by using as little water as possible with each flush. So putting a hose on the Flush King and pushing water into the clog broke it loose.

This was the foundation of my experiment, because I was not worried about the possibility of a clog. I also knew that our rig rides a little “nose-high” when we’re hooked up. Not a lot, but a little. And I know that the outlet for my black and gray tanks is rear-facing. And finally, one of my favorite gadgets, the water meter.

This uses garden hose threads and can go anywhere inline between the spigot and your rig, and you can use it to keep track of how much fresh water is going into your rig. It’s incredibly handy to be able to know this stuff. You can use it when filling up your fresh water tank, you can use it to keep a running total of how much water you use in a day, or a week. And, if you want to know how much capacity a tank has, you can zero out the counter, and fill up your completely empty black or gray tank, and once it’s full, the meter will tell you how much it holds. If you have, for example, a 50 gallon gray tank, and you do this, and it takes 45 gallons, that means you have 5 gallons of gunk. (This is assuming that you are getting an accurate reading. The way to test that of course, is to fill something like a five gallon bucket, or a 1 gallon jug, and see if the meter is accurate. I’ve lost 4 of these things by forgetting to take them off the campground spigot, and they’ve all been accurate.)

So my method was to empty the gray tank completely right before we hit the road to travel for 5 or 6 days. Normally I try to travel with at least a half tank that first day to get some good sloshing going. But in this case I completely drained it and left the gray valve open, but closed the Flush King valve. We hitched up and drove all day, at least 6 or 7 hours. When we arrived at our campground I hurried back to the outlet and saw that the clear plastic pipe was indeed completely full. During the drive, what was in the gray tank had slid out and down the line and stopped at the valve. I hooked up a sewer hose and pulled the Flush King valve open and…….nothing. Nothing happened. I looked closer and saw that what I thought was gray water with a lot of white flecks of grease and food bits in it was actually more like a really, really, REALLY thick milkshake, or like a sediment sausage. It was just sitting there and not budging. I gave it a minute and just when I was starting to think I might need to start putting some water down a sink drain or maybe hook up a hose to blast from the outside, it verrrrrrry slowly started to ooze out and down the sewer hose. It took forever, because it was mostly sludge and hardly any liquid, but gravity eventually pulled it down into the hose. And there was a lot. I would say that there was at least 2 feet of that sludge that had to drain out and then it took rinsing some water down the sewer hose to break it up and speed it down the drain. I wasn’t really worried, because although it was dense, it wasn’t packed, and although it wasn’t really wet, it wasn’t dry either. It just took a while for it to move. I then closed the Flush King valve, but left the gray valve open, because I didn’t want to pack any gunk that might be sitting in the gray valve into the seal. We took showers and did dishes and I did laundry and once the gray tank was as full as I could get it, I opened the Flush King and let the “whoosh” do it’s job and then closed the gray valve. I did the same thing the next travel day, and got the same result, but with a shorter “sausage” of goop, and it was not as dense. On the third day there was nothing but a few inches in the flush King. So after almost 5 years, I probably drained three gallons of sediment, but that doesn’t mean much, because we spend the vast majority of our time sitting still, which I think contributes. I have noticed that whenever I “slosh” the gray tanks when we’re traveling what comes out is so dark it’s almost black. (Interestingly, a friend of mine recently bought a very old rig and had this same experience and just told me about it the other day!)

My conclusion on this is that this is something you shouldn’t worry too much about, and maybe do it as maintenance step every year, or maybe even every two years. For Jami, who has a 2001 and isn’t the original owner, I would say not to lose any sleep over it while you wait to start traveling again, but as soon as you start to travel, consider starting to work on clearing this stuff out. Not because I really think it’s that big of a deal, but you will get peace of mind, which isn’t nothing.

I highly recommend doing it while driving over the course of several days, so you aren’t living in a rig that’s jacked up all day waiting for this stuff work it’s way out. And only when you are going to be on full hookups at the end of each driving day so you can get more water in the system to keep anything from drying out. Tanks that are in constant use are always wet, and gray tanks get filled faster and more frequently so you don’t have to worry about this stuff hardening, but it IS a good idea to try to keep the tanks as clean as you can, at least in my opinion. Once we started traveling in a few weeks I will be doing this again because I want to see how much has accumulated in a year, and I also want to get some pictures and maybe some video with which I will update this post. Thanks again for the excellent question, Jami, and hopefully this is helpful.

If anyone else has any questions, please feel free to ask them in the comments!


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9 thoughts on “Holding Tank Treatments

  1. Oh my god, my head is exploding! Everything I’ve tried to learn in my one season of RV’ing – gone, just like that. I – I don’t know what to believe anymore. Maybe the world isn’t really round . . . . ? But seriously, thanks for the informative post – I’ll share this with my tank guy, and we’ll have a serious tank talk. 🙂

    • LOL. All I can say is I have never met anyone who spends more time obsessing about our tanks than Lee. You know I tend to present all sides but I 100 percent trust him in this and have seen first hand what he says is true.

  2. Good info Lee ! I was just reading about the gray tank water and the heavy particles that sit on the bottom of the gray tank and how they can thicken as time goes by. We use a scope type water hose you stick doen the toilet to make sure we’re getting every last bit of nasty out, and it works great. As for the gray tanks, we have 2, the hose won’t fit through the sink catcher and definitely if it did, wouldn’t go pass the P traps. I was wondering if you had any suggestions for this. We recently bought a 2001 5th wheel in great shape, one owner, and used maybe a few times a year. we are full time, stuck in Florida ( the heat is unbearable , I know what Tracy meant about Texas ) We normally leave Florida the beginning of June, and return the end of September. ( We keep our site all year long ). With staying put due to the pandemic, both myself and hubby are high risk, the mixing of sludge going down the road isn’t going to loosen up grease, particles of food, anything that escapes the paper towel or drain stopper this year because we are sitting still. Do you think that there is a way that would work to break up the goop or pour a bucket of water, with more power then the faucet can deliver would work. I just want to know that my tanks are free of sludge. This is a 2001 and I don’t know what or how the original owners treated the tanks. And I’m done buying treatments for the tanks, thanks for that info! You both are awesome !!

    • Regis – My feeling on microbes, bacteria and enzymes is the same as everything else; they’re a waste of money, and no substitute for just keeping the tanks rinsed well. Most people empty their black tank every 10-14 days, and it takes time for living things to work their magic. There’s also the issues of temperature. The beneficial bacteria die at around 85°, AND they need time to do their work, so to me they’re double useless. I spent a couple of hours looking at more or less every product out there, and reading as much as I could get my eyes on. Guess what was always missing? How LONG it takes for the product to work and to get the job done. So they can legally make all the claims they do but leaving out the time variable. If the claim ended with “after 30-90 days” nobody would buy the product for this purpose. My favorite part is how the packaging tells the consumer to increase the dosage if the product isn’t working. Great way to sell product. – Lee

  3. I agree with everything you posted and I do want to try the gray tank with slosh water then dump technique. I will say that I’ve had very good luck with a toilet wand that I made using pvc in the black tank. I use it two or three times a year and it is amazing how much extra ‘stuff’ I get out. I then can shine a flashlight down the toilet drain and see clean tank floor with no buildup. Even the tank sensors seem to work better for a while after that. Would love to hear your thoughts on that Avenue.


    • Russ – I lie awake at night dreaming of a blank tank that I could get to with a wand. In a previous post I think I mentioned that ours is offset, so there’s a 45° angle pipe between the toilet outlet and the tank. So I can’t see down into my tank. For anyone who has a straight shot, almost ANYTHING will help. Some people fill up their bowl and then flush it and get a nice hard WHACK of 3 or 4 gallons hitting the tank, or putting a hose down and just blasting away. I’ve also heard of people running hose directly from the pedestal into the bathroom and down the toilet because the water pressure directly from the pedestal is usually greater than anything inside the rig. I think all of those are great ideas, because they allow you to really pound water pressure in there. For anyone who has a straight drop, this is a game changer, but I think I would still fill and dump rinse a few times, just to be sure. Try it both ways, and let me know which one works faster! For those of us poor suckers without, we have to go the long way round. – Lee

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