Make Your Own RV Black Tank Cleaning Bombs

Ah, the RV black tank. It’s everyone’s favorite topic. Because who wants an awesome RV tailgate to end up in the shitter because of a black tank clog?

In order to avoid a disaster of epic poop proportions, you’ll need to maintain your RV black tank and we have the solution for you.

It’s cheap, it’s DIY, and it’s easy!

Want a better way to clean your RV black tanks? Try these RV Black Tank Cleaning Bombs!

RV Black Tank Cleaning Bombs

Disclosure: This post contains affiliate links for various products below. You get the same low prices and we earn a small commission.

If you hang out long enough in the RV groups, you’ll see cross-over with tiny homes and quite a bit of frugal living sites. Something about the RV lifestyle lends itself well to these groups.

And popular among all of these groups is a certain do-it-yourself mentality.

Even for cleaning products.

Which is how I found out about toilet bombs.

I had heard of bath bombs before and these are basically the same thing. You drop them in some water, they fizz up, do some magical cleaning action and then you flush the toilet bombs away. All good.

And naturally, I was like “this is easy! I can do this” and “I wonder if they would work in the RV black tank?”

This innocent of questions lead me to an entire night of scouring the interwebz to see if the components would work in RV black tanks.

The Geo Method for RV Black Tanks

There are a few basic methods for keeping black tank odors in line. You can buy chemicals at Amazon or Camping World. Or you use the Geo Method.

The Geo Method uses a couple of basic household components – Calgon water softener and Borax laundry booster. You mix all of these in the tank. The Calgon keeps waste solids (yes, the eeewww stuff) from sticking to the sides and building up in the tank. The Borax cleans it all up.

But I’m always looking for a better way.

Plus Borax is also a water softener? That means you are doubling up on water softening by using Calgon too.

Enter… the toilet bomb!

See Also: RV Waste Tanks Explained

Toilet Bombs for the RV Black Tank

RV Toilet with toilet brushMost of my RV use comes during football season, when I’m taking the RV out sometimes weekly. I’m also dumping weekly. With so much going on, I continue to look for ways to make things easier.


Less of a hassle.

So instead of having to haul several different containers out, why not have a handy little “ball” of stuff to throw down the toilet during the weekly cleanup?

If you’ve been using the Geo Method, you’ll already have two of the ingredients on hand needed to make RV black tank cleaning bombs! The Borax and baking soda. The third ingredient is citric acid.

See Also: How to Poop in an RV (aka How to Use the RV Toilet)

Citric Acid in the RV Holding Tanks

I can hear you from here:

“Oh, acid! We can’t be putting that in our tanks! It’s not safe!”

Have no fear! Citric acid is fine for your RV tanks.

First, it is naturally occurring in lemons and limes. Citric acid is edible and can be found in a lot of foods you eat or drink, like soft drinks or baking in place of lemon juice.

Ever had sweet and sour candy? That white sour flavoring is… yep, you guessed it – citric acid. You’ll also find citric acid in many ice creams. It is used in canning operations (you know, those mason jars you love to paint and use at your Southern tailgates).

If you look at the ingredient list on many of your beauty products, you’ll find citric acid. Shampoos, chemical peels for your face, and many body scrubs all have citric acid.

Citric acid is also commonly used as a cleaning agent for membrane filters in water treatment process.

It’s also used to remove lime buildup in boilers and evaporators. Many boaters recommend using citric acid to clean fixed fresh/drinking water tanks. As a natural ingredient, citric acid typically has no bad effects on lakes when the tanks are emptied.

It is even used to clean aquariums (where trace residue of other cleaning products could be lethal to fish).

Citric acid is a common ingredient in those commercial black water tank cleaners. Even the makers of RV Digest-It recommend using citric acid to remove calcium buildup in your black tank:

If you are traveling in a hard water area you sensors will likely stop working because of calcium buildup on the sensors. If you catch it early RV Digest It should be able to break down the greases and oils that cause the calcium to stick to the sensors, however it it’s been building up over a long period of time the bacteria may not be able to penetrate the calcium if this is the case we recommend putting citric acid in your tank for a day or two and then empty and rinse the tank to remove the calcium.

It’s considered a relatively weak acid. But it has great power when it comes to cleaning.

All in all, that was a long way of saying: citric acid is safe for your RV black tank! And you’ve probably been putting some in your tanks all along.

(You can buy citric acid at Amazon in larger quantities than you can typically find at your local grocery store. And cheaper too! Might as well get the baking soda and Borax while you are at it.)

See Also: Maintaining Gray Tanks: The Other RV Waste Tank

Make Your Own RV Black Tank Bombs

Without further ado, let’s make the best homemade RV holding tank treatment!

Buy these products on Amazon: citric acid, baking soda and Borax.

Add all the dry ingredients in equal parts into a ziploc bag or small bowl and mix well.

Then add the smallest amount of water possible, just enough to get them moist (all, love that word! haha)

You’ll notice a bit of fizzy action when you add the water. This is normal.

The key here is to keep the water to a minimum. Use only the smallest amount absolutely necessary to get everything to stick together.

Otherwise, the final product will bloat in the molds and won’t be all pretty like. You’ll still be able to use the toilet bombs but they won’t be neat little balls that you can drop down the toilet and into the black tank. Or they can take a really long time to dry out.

Your best bet if this happens is to crumble them up and then shake into the toilet as needed. Also great for using in the gray tanks.

Wet RV Black Tank Bombs in silicone moldsAnyways, back to making our RV toilet bombs. After you add the water, you’ll want to put the paste-like mixture into silicone molds. I’m partial to the ice sphere molds, mostly because I already had some for my whiskey drinking ice. But really, any silicone mold will do. You can get all sorts of creative if you want!

Fill up your molds and then leave them alone until the paste dries solid. Then you can pop them out, store them in an airtight container, and drop them in your RV toilet after each trip to the dumping station.

If you want to skip the molding step, you can also keep all the dry ingredients mixed up in a small shaker bottle. I’ve got an empty Bounce Bursts bottle (for those small smell good satchels) that is perfect for this – even has the handy cap to measure it out.

Using the RV Black Tank Cleaning Bombs

RV Black Tank Bombs out of silicone molds on RV kitchen counterAfter you have dumped your black tanks, just drop one of these RV black tank cleaning bombs into your toilet.

Let it fizz up with the water in the toilet (and clean the toilet) and then flush it.

Make sure there is a good layer of water in the black tank, just like you’d do with the Geo Method.

The cleaning bombs will continue to work, scrubbing away at the gunk inside your tanks. It’s even better if you drive the RV around, to get the agitation like you would in a washing machine or dishwasher.

Like all other things that you use around the RV, a little goes a long ways. No need to put buckets of this down the drain.

Use only one cleaning bomb until you determine that you need a second.

Sometimes though, if you are RV boondocking or otherwise going long times between dumps AND it’s hot summertime weather, you may find that you want to drop a second bomb into the RV black tank when it is about half way through. This can definitely help with the smells that will become harder to deal with in the higher temps.

Works in the Gray Tanks Too

These Black Tank Cleaning Bombs work great in your your gray tanks as well. Thus, RV Black Tank Cleaning Bombs are truly RV Holding Tank Cleaning Bombs.

Fill the sink or shower basin with some water, drop a cleaning bomb in it (clean the sink or shower) and then drop it into the gray tank.

Keep a little water in the tanks, even while the RV is in storage between trips. This will allow the components to keep cleaning the tanks and keep the seals moist.

See Also: Tips to Help You De-Winterize Your RV and get ready for spring camping and tailgating

These Cleaning Bombs Work at Home Too!

The cleaning bombs also work great for your bricks and sticks toilets. Just drop one it, let it fizz for a little while and flush away.

If you are using these cleaning bombs for your home toilet, you can also add drops of essential oils for added odor control. I figure though that the essential oils aren’t necessary for your RV black tanks.

The RV black tank cleaning bombs also work great in your dishwasher.

See Also: Essential Gear for RV Sewer Systems

Try It and Let Us Know if the Cleaning Bombs Work For You!

RV Black Tank Cleaning BombsSo now, why don’t you try these RV Black Tank Cleaning Bombs and let us know if they work for you. Comment below!

You may find that you like this homemade RV holding tank treatment better than other RV black tank methods.

Buy these ingredients on Amazon:
Citric Acid
Baking Soda

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Black Tank Cleaning Bombs

Yield: 9 Cleaning Bombs
Active Time: 5 minutes
Total Time: 5 minutes
Difficulty: Easy

Make these easy cleaning bombs to keep your RV black tank working in pristine condition.


  • 1/3 c Borax
  • 1/3 c Baking Soda
  • 1/3 c Citric Acid
  • 1 tsp. Water


  1. Mix Borax, baking soda, and citric acid dry ingredients in a gallon size Ziploc bag. Mix well.
  2. Add several drops of water, to allow ingredients to bind together. Mix well. May need to add several more as you go. Do NOT over-wetten (that's a word, right?).
  3. Pack tightly into silicone molds. Let dry overnight.
  4. Pop out of molds. Let the RV Black Tank Cleaning Bombs continue to dry for 1-2 days.
  5. Store in air tight container until used.


The key here is to keep the water to a minimum. Use only the smallest amount absolutely necessary to get everything to stick together.

If exposed to air during storage, the bombs will absorb moisture from the air and may stick together or become difficult to remove from the storage container (if odd size top)

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  1. Tried making these today, and the bombs keep expanding out of the molds. What am I doing wrong. I punch them back down but they have risen out of the mold and onto the countertop every time. I made 3 batches, each time using less water but they have all reacted the same way. Do you know if they will they still work? Thanks

    1. Hi Dawn! It really is the amount of water that you used. You really want to use only a couple of drops, just enough to get the dry ingredients to stick.

      The good news is that they still work! They just are not the cute little bath bomb like creations. You can just crumble them up and drop them in the toilet, sink, or shower, like you would if they didn’t expand. When they hit the water, you should still see the fizzing action. I always like to let it sit in the toilet for a minute to clean the toilet. 🙂

      If you still can’t get them to work, just mix up the dry ingredients really well and put them in a shaker. I like the Bounce Scent Booster shaker since it has a measuring cup on top. Then just dump a small amount into the toilet directly. Confession: a lot of times I don’t even make the toilet bombs and just use the dry ingredients!

      1. Hi! Thank you so much for this recipe. If I were going to just dispense the mixed dry ingredients rather than make the bombs (and I don’t have a Bounce Burst bottle), how much would I measure out to use per cleaning? And by using these, I shouldn’t need to use the Calgon? Thanks for all of your help! 🙂

        1. Hi Christa! Thanks for stopping by and I’m happy that you found the recipe useful.

          Exactly how much to use is going to depend on the size of your black tank. I’d start with about a quarter of a cup and see if that works. If you notice odors or anything like that from the RV black tank, you will want to increase it.

          I typically don’t need to use Calgon for my black or gray tanks. It’s a water softener, so if you are having trouble with hard water it may still be necessary.

          1. Thank you for your quick reply! We had been using the Calgon as part of the Geo Method to keep waste from adhering (I think that was the function of the Calgon if I remember correctly), so I wasn’t sure if we would still need that step with this recipe.

          2. So I learned something new today while I was researching points about the latest blog post (How To Remove RV Sewer Flies and Gnats) – Borax is a water softener, not just a laundry booster. So the Borax in the recipe will do the same thing that the Calgon does in the Geo method. (I’m not sure if I knew this before or not, but if I did, I was reminded of this fact today).

            If you have some Calgon leftover though, don’t throw it out! You can replace the water in the recipe if you make the black tank bombs (instead of the dry components). This will provide enough moisture to keep the ingredients glued together until you are ready to use them.

      2. Do you use the bomb method to treat black holding tank after each time it is drained or just when needed to specifically clean the tank? Does it keep down odors until tank is drained again? I typically go a week to 10 days before tank is full then drain. I have used and experimented with Happy Campers, RV-digest it, and Tanktech RX which I add for in-between flush periods.

        1. Terry,

          I treat it every time I dump the tanks (well, after dumping and rinsing the black tank). I’ll add more on occasion if the need arises – like I’m going longer between dumps or the smells get smellier.

          I have found that this method does help keep the odors down. The baking soda does a very good job of that without it being too perfumey (yep, that’s a word despite what my spell check says). I’m not a big fan of lots of different scents, especially in the small space of an RV bathroom. My bath products are more than enough!

          Let me know if you have any more questions.


    2. I use a small spray bottle. I have a recipe for a toilet fizzy includes essential oils vinegar and hydrogen peroxide would it be safe for RV use?

      1. Debbie,

        Hydrogen peroxide should not be mixed with vinegar in the same bottle. It creates a toxic acid that could irritate the skin, eyes, and respiratory system.

        Either ingredient on their own would be OK for RV use.


    1. Hi Barbara. I have never used the blue enzymes in my tanks. Prior to the Tank Bombs, I used the Geo Method (Calgon water softener and Borax laundry booster) to control the odors and keep things running smooth in my RV tanks. The Tank Bombs replace all the other chemicals and cleaning agents that you would place in the RV black tanks.

    1. Barbara, depending on the size of your tank, probably 1-2 tablespoons. It may take a little experimentation to get it right, just like you probably did with the Geo Method.

  2. Would it be safe to add some boiling water after flushing the toilet bomb and running few gallons of water. We have noticed some drain flies and are trying to get rid of them. Boiling water seems to help and hopefully getting the tanks clean with this method will solve the problem.

    1. It should be ok to add boiling water to the tank. As it cools, the extra water will help keep the sludge from forming the Big Pile of Poo Doom!

  3. so if you add this after you dump the tanks am I correct that you leave the bomb plus some water in the tank – that it stays until the next time you use the RV?

    1. Hi Shannon! Yep, that’s exactly what I do. Dump the tanks. Then add a little freshwater to line the bottom of the tank and drop one of these in. Use the tanks, empty and repeat.

    1. Jennifer, I typically do not use a water softener. The Borax is a multi-purpose household cleaner that removes hard water deposits. Make sure to add water when you drop them in the black tanks so that the Borax can dissolve.

  4. I made these and noticed that you don’t need drops of water. I put the mix in a bowl and squished with my hand to break up the chunks of the borax. After about a minute or two – you have to be patient – that is the key here, the mixture did get some moisture to it and was moist enough to put in molds. YOU DO NOT NEED ANY WATER. Just WAIT – then pack them tightly in the molds and they won’t expand.

    1. Wait, who has patience? 🙂 Just kidding.

      A lot will depend on the humidity when you make the black tank cleaning bombs on whether you can just wait for them to absorb the water from the air. If you are in the desert, don’t depend on it working well. Unless you’ve just taken a shower in your RV or something like that.

      But you do bring up a good point, that you don’t need a lot of water to make the cleaning bombs. Just a little bit goes a long ways.

      Thanks for trying them out! Hope they work well for you. I know that they really keep the smells in my black tank down and my black tank sensors still work.

  5. If a black tank needs revitalizing including getting sensors to work, how much should be put in with a full tank?

    1. It will depend on the size of your black tank. For mine, I use a golf ball size Black Tank Cleaning Bomb unless it is just giving me lots of problems lately (usually smell) then I’ll drop two in. But I do this at the beginning of the cycle, before it is full. Drop the cleaning bomb in, add some water and then go on. If it gets to smelling before it is time to dump, I may add the second in with some more water.

      Because I am an RV tailgater, it means that I am constantly on the move between games and stadiums (and some cool parks and RV campground spots). This movement is great to help keep the RV black tank in good working order. It allows that water + cleaning bomb to slosh around, cleaning the sensors and washing down the sides. That is really the best way to keep the RV black tanks in good working order – water + cleaning bomb + movement. And using the RV black tank back flush system.

  6. Kimberly I can’t wait to try this.
    We are in tag axel motorhome. Our black water tank is 51 gallons. How much should I use?
    Thanks in advance for your reply

  7. Thank you Kimberly. I am just starting to use the mixture.
    Can I use plastic ice trays? I did notice it began to stick together overnight without any water.
    One more question, can you suggest how to clean the grey water tank sensor. We closed it off, I put the mixture in it and drove from one campground to another and emptied the grey water tank. Still says 2/3 full.
    Thanks in advance for your help.

    1. Sherry,

      On the gray tank sensors, it is definitely harder to get them cleaned up because there are rarely gray tank rinse systems, like there are on the black tanks. And there is no easy way to get to the tank like straight down the toilet for the black tank. There are lots of P traps and often Hepvo valves that make it impossible.

      If the black tank bombs didn’t work, your best bet is going to be another product that I highly recommend: Bio Clean. It’s septic safe but really gets at the stuff in your tanks. Fill up your gray tank and then add the Bio Clean. It helps if you have warm (not hot) water in the tank to let the bacteria do its thing.

      Also, like with the black tanks, keep the gray tank valve closed. When you let the water build up, there is a certain amount of force that comes with dumping the tanks. It helps to get the stuff off the sensors.

      I would suggest silicone over plastic ice trays to make them easier to remove. But yes, you can use ice trays for the black tank bombs.


  8. Can I leave the mixture in the tanks while in storage? I had a bad calcium/lime buildup in my black water tank and after reading your post, I added about a cup of citric acid to a half full tank of water and left it for a week, drain and flushed the tank and it was full of a sand like substance.I then refilled the tank with water and added another cup of the citric acid, borax and baking soda. Is it safe to leave that in the tanks while in storage or should I drain and flush.

    1. Joe,

      I have left the Black Tank Cleaning Bombs in my tank (with some water) during storage without any problems. It is actually quite good to help any leftover substances (say toilet paper) to dissolve in the water. And the water keeps the seals from drying out which can cause leaks and other problems later on.


  9. Kimberly, Thank you so much for your reply. I have also been thinking that if the black water tank was full of a lime/calcium build up then where did it come from? Most likely from the well water in most camp grounds. And if this is the case wouldn’t the fresh water tank have the same issue? And maybe I should clean and flush the fresh water tank the same way????

    1. Joe, It is entirely possible that the lime/calcium build up came from the fresh water in campgrounds. Whether you need to do anything on the fresh water tank will depend on whether you fill the tank. A lot of people, if they are spending significant time in a campground, will only use city water and not fill their tanks. But you could also get a build up in your water heater.

      You probably don’t want to put some harsh chemicals in your fresh water system. You could definitely try adding citric acid since it is a relatively weak acid. Another popular choice would be vinegar. About 6-10 gallons of regular white vinegar should do the job. Do it basically the same way you would sanitize the fresh water system – pour it in, open faucets to get the vinegar spread through all the pipes, and let it soak. Then drain and rinse.

      Don’t forget to check your shower head if you have had hard water problems. It is easy to clog up the shower head. Soak it in vinegar.


    1. Carl, the Black Tank Cleaning Bomb is the only thing that I use in my RV black tanks! Obviously, I think they are the best 🙂


  10. After trying this several times and having a huge mess on my hands, I tried it with no water at all. As it turns out, it is humid enough here to leave it to sit for a day or so and …PRESTO! nice hard cubes that popped right out! I live in Austin Texas and did it in August. I put the cube maker out on my patio table and it worked perfectly.. I figured if it didn’t work, I’d just put the plain powder in the tanks…but it did!

    1. Ann,

      Great! Some places (and it can vary by time of year) can be very humid, definitely enough to make the ingredients mold together just from the air.

      But if it is that humid, make sure you are dehumidifier in your RV! You don’t want mold forming!


  11. Very helpful, thanks so much.
    Want to know how long it will take for the combination of dry ingredients to expire , if I want to use just the powder?

    1. I haven’t found an expiration date yet! 🙂

      Do keep the RV Black Tank Bombs in an air-tight container though. If not, just the humidity in the air is enough to make the hardened bomb over time. And then when they hit the water in the toilet, they will actually explode and make a mess. Ask me how I know.


  12. I live in my Grand Design Reflection travel trailer full time and parked so I can’t move it around to get the slosh effect of a washing machine in mine. This 100 plus degree weather we are having this summer us making my black tanks stink some kind of awful every time I flush. I’m having to dump my black tank frequent during to smell. My question is can I add the bomb to my tank while using to keep smells down? I did my first batch yesterday and dropped a few in there after dumping and let it soak for a while before flushing the tank and it still smells.

    1. Joy, this summer heat is brutal and no joke! To answer your question, yes, you can add extra as you go along if needed. Hope that helps. And remember, it’ll cool off at some point. Hopefully soon.


  13. We have a houseboat and our black tank is pumped every two weeks. The heat this summer is relentless. Do you think using the bombs during that two week span would help with the smell after flushing? Or should the bombs just be used after dumping? Thanks

    1. Kelly,

      I agree – this heat is relentless. I have found that adding the RV Black Tank Bombs between dumps does help. Good luck!


  14. I’m just curious…..will these bombs deteriorate the ball gasket or slide gaskets that hold some water in the bowl?

    1. The cleaning bombs don’t “live” in the toilet bowl. They go into the black tank, so they won’t affect the gaskets that keep the water in the bowl. If anything, the RV Black Tank Cleaning Bombs are going to be safer than most chemicals, including bleach, that you would normally use to clean toilets and bathrooms.