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RV Black Water Tank Clogged? Here Are Easy Ways To Unclog It!

Kelly Headshot

By Kelly Beasley

Published: October 5, 2021

Last Updated: November 12, 2021

A toilet back up in your camper is probably one of the most unpleasant aspects of RVing!

It doesn't have to happen, and it's preventable.

But if you're reading this, I'm guessing you already have a clogged black tank, my friend!

Kelly slapping her forehead

Bummer for you. The good news is that all waste clogs are fixable. (As long as there are only four things in your dump tank: water, urine, toilet paper, and bowel movements!)

It would be best if you put down no other solids or other waste types into your RV black tank.

Don't worry. In this guide on unclogging an RV black tank, you'll learn all you need to know to diagnose, remedy, and best of all, FIX your clogged RV toilet.

Read on to learn how to unclog an RV black water tank.

Types Of RV Toilet Clogs

The things that clog an RV toilet are any combination of these three things: toilet paper, solid waste, and hardened solid waste.

That said, there are three ways an RV toilet can clog:

Pipe Clog

Your RV toilet's drain pipe leads from the toilet's base and moves all waste down into the black tank.

Sometimes it's a vertical pipe, and other times, there are bends in the waste pipe as it heads down into the black tank.

Most often, a pipe clog happens in the type of RV toilet setup that has twists and turns in the pipe.

If the black tank is not directly under the toilet, bent elbows (turns in the pipe) are required to get the sewage into the black tank.

This is where the problems usually occur.

Typical mistakes that clog a pipe are:

  1.  Not using enough water in the toilet bowl for flushing.
  2. Using too much toilet paper or non-septic-safe toilet paper.
  3. Large or hard bowel movements (seriously).

Poop Pyramid

This one is just as it sounds. It's a pyramid-shaped pile of your poo down in the black tank.

This is always caused by a novice RV owner leaving the black tank valve open while parked and connected to a dump (most likely when you are at an RV site with full-hookups).

Keeping the black tank valve open when connected to a dump allows the liquids to escape out of the black tank. Meanwhile, the solids remain where the land when coming out of the pipe from the RV toilet.

(The solids you flush down the toilet require a certain amount of liquids in the tank in order to be removed/drained.)

There's your poop pyramid. Eventually, the pyramid grows so tall it touches the toilet pipe until finally, your toilet can't drain into your tanks.

Compacted Tank Or Hardened Solids

It's not super likely, but it's possible that if you don't use enough liquids, a mass of solid matter could accumulate at the bottom of your RV toilet holding tank.

Similarly, if you store your RV for long enough with contents still in the RV's black tank, the liquids will eventually evaporate out.

This practice leaves the solids in there, and eventually, at worst, they will dry and harden. (Remember, there's a vent in your blackwater RV holding tank. So, it's not sealed tight.)

So My Black Water Tank Clogged. Now What?

Toilet paper rolls making face on RV toilet

The next step is to determine which type of clogged black water tank you have. (Pipe, pyramid, or compacted.)

Whichever type of clogged black tank problem you have determines what steps will unclog the blockage.

Three signs that hint at what is going on:

  1. Nothing goes down your RV toilet anymore when flushing.
  2. Very little or nothing drains from your RV black holding tank when you dump.
  3. You have both problems.

It's an excellent idea to have a clear RV sewer hose adapter so you can see how much is or is not draining from your black holding tank.

How to figure out what these clues mean:

  1. Poop Pyramid: Nothing will go down the toilet bowl, AND nothing (or not much) comes out when you dump. You are guilty of leaving the black tank valve open while connected to the sewer. You have a poop pyramid.
  2. Clogged Pipe: Nothing will go down the toilet, and nothing (or not much) comes out when you dump. You did NOT leave your black water valve open while parked.
  3. Compacted/Dried Up Tank: You can add liquid into the toilet, and it flows into the camper blackwater tank, but nothing comes out when you dump. You did not ever leave the black tank valve open while camping/connected to the sewer.
  4. Misreading Tank Sensors: Here's one you may not have thought of. Your sensors say your black tank is full, but you just dumped it. If all works just fine (you can dump just fine, and toilet contents drain into blackwater holding tank no problem), but the RV black tank sensors read otherwise, your sensors are giving inaccurate readouts (VERY common problem).

How Do You Unblock An RV Black Tank?

The method you'll need to utilize to unblock your black water holding tank 100% depends on what type of blockage you found.

Here we share with you the fix for each.

How To Unblock A Poop Pyramid

To unblock pyramid plugs, first, you must diagnose that it is indeed a poop pyramid causing your tank clog.

Three things determine a pyramid is clogging your toilet:

  • You left the black tank valve open while connected at a campsite.
  • Nothing (or very little, or it goes very slowly) goes down the toilet anymore.
  • Nothing comes out through the sewer hose.
  • You MIGHT have noticed the RV toilet draining slowly before it stopped draining altogether. It will start draining slow before the poop pyramid starts to block the pipe completely.

If these three match up with your situation, congratulations! You have a poop pyramid.

Here's how to unclog an RV with a poop pyramid.

You can try a few methods. Your main goal is to open up a channel where you can get water into the tank to fill it up. Here's what you should do first:

  1. First and foremost, CLOSE your black tank valve.
  2. Pour some liquid plumber type of enzyme RV black tank treatment into the toilet. It might do the job of breaking solids down so that a channel opens up. Leave it as long as the manufacturer says. This is likely to be a few hours and up to a few days.
  3. If a channel opens up, fill the tank with water and an enzyme treatment that will go to work breaking down the waste buildup.
  4. If no channel opened up, you must manually open up the offending plug. You can do so with a PEX pipe (similar to a toilet snake), which is flexible. Stick it down the toilet and move it around. If all goes well, the stubborn stuff will open up. Once open, proceed with #3.
  5. Remember, you MUST let the product sit for a minimum of what the manufacturer says. If you can go a little longer, probably even better. Give the product time to break down the solids.
  6. After the allotted time, flush out the clogged RV toilet tank. Everything should be dissolved and flow freely.
  7. Even if everything seemingly flowed, it's a good idea to repeat the process at least one more time to be sure you got the entire pyramid dissolved!
Kelly's RV toilet

How To Unblock A Compacted Black Tank

To unblock a compacted tank, first you must confirm that indeed it's a compacted RV holding tank.

Here's what determines that you have a compacted tank:

  • Liquids flow in when you're flushing water down the toilet.
  • Nothing comes out when emptying the clogged RV black tank.
  • NOTE: If liquid DOES come out when emptying the tank, you probably have misreading sensors and NOT a clogged black tank.

So now you know how to unclog an RV black tank. Be aware that this type of clog might take a little more to eliminate (no pun intended).

This is especially true if you stored the RV without dumping your blackwater tank. The solids are now hardened at the bottom of the tank.

You might need 2-3 times to get it completely clear.

Here's how to unclog an RV with a compacted blackwater tank:

  1. Fill up your blackwater tank full of water.
  2. Pour in your chosen enzyme treatment. The manufacturer may want you to use the entire bottle.
  3. Leave it in as long as the manufacturer says. Longer is better. Letting it sit overnight at minimum is preferred.
  4. After the allotted time, try dumping the tank at an RV dump station.
  5. If no liquid waste comes out, leave it for longer.
  6. Drain the blackwater tank at the dump station. Repeat if you think there are still bits left behind.

Liquid Tank Unclogger

All three of the ways to unplug an RV holding tank call for some sort of liquid enzyme treatment to assist with the process. You may want to try the Unique brand tank cleaner as it's specifically formulated to deal with clogged pipes, poop pyramids, and a compacted tank.

Unique tank cleaner

How To Clear An RV Toilet Clogged Pipe

This type of RV toilet tank clog might act like having a poop pyramid.

However, if you DID NOT leave your blackwater tank open while connected to a sewer, and you DO NOT have a black RV tank leak anywhere, a toilet that won't drain out the sewer line means a clogged pipe.

Here's how to unclog an RV with a clogged toilet pipe.

  1. Try plunging it. If the pipe is indeed clogged, this method works. Still, it may not push out the blockage.
  2. If that doesn't work, pour your enzyme treatment down the toilet and let it sit for the time the manufacturer says to leave it.
  3. After the time allotted, flush and see if it works. If not, try plunging again. Repeat the enzyme treatment until it successfully eats through the clog.
  4. If it still won't flush, get yourself a PEX pipe and try pushing it through into the black tank.
  5. Once the clog clears, fill your tank with water and flush to get any remaining 'stuff' out.

How To Maintain A Healthy Black Tank

Congratulations! Now it's time to figure out why you had a clogged black tank pipe and learn what it takes to prevent future clogs.

Here are the conventional ways to avoid a clogged toilet:

  1. Use septic-safe toilet paper.
  2. Rip up your toilet paper before using it.
  3. Use lots of water with your BM flushes (How much water? Fill the bowl at least halfway. The more water, the better).
  4. If you are constipated or have hard stools, you might have a problem. Hard and/or long stools can get stuck. Cut these if/when they happen. Disgusting? Yes. Effective? Also yes.
3 rolls toilet paper on RV toilet

DEMONS!!!! LOL 

The best way to prevent a blackwater tank clog is this: Do NOT put your toilet paper down the toilet. Instead, put it into a wastebasket.

It sounds gross, but it's not AT ALL. I (Kelly) have not been dumping TP down my toilet's plumbing for about 5 years, and I have never had a clog.

Better yet, I can use any brand of TP I want! Finally, it saves tank space when you're boondocking, so that you can stay out longer before having to dump.

OK, enough preaching.

Hopefully, you'll use septic-safe TP and more water than before, and you'll never have any future clogs in EITHER of your tanks.

Now that you know, you can prevent one from happening easily with this regular maintenance of your black tank.

Regardless, I hope you never have to deal with your human waste in this fashion again!

How To Unclog A RV Toilet Holding Tank- MYTHS!

I am including methods I've seen others claim work by doing a Google search.

Some of them are downright ridiculous. But here we go:

Ice Method

This simply doesn't work to dislodge anything from your black water tank. If you tried it and it worked, it was sheer luck.

Ice cubes closeup

 If you have a clogged pipe, water and ice aren't going to be able to get up there to dislodge it.

If you have a poop pyramid, the only 'rubbing' the ice will do is very minimal and only in ONE level of the clog.

If you have a compacted tank, well, floating ice won't even touch the stubborn waste.

Boiling Water

OK, help me out with this hot water method. HOW is hot water or boiling water or even warm water going to break anything up?

It doesn't have the ability to eat/remove anything. I can't believe I even read this as a 'solution' on another website. Hot water? Please.

Good for grease clogs? Maybe. Good for poop clogs? Nope! (Unless you eat a lot of grease maybe? 😉 )

Vinegar and Baking Soda

Again. Please. Maybe try pouring this onto some dog poo and see what it does. It will be a whole lot of nothing. Don't waste your time.

If you think some tiny bubbles are going to move sh**, you're wasting your time. Besides, the reaction that causes the bubbles lasts for a very short time.

No, this one is not going to work. (Though it's a great way to make a volcano!)

Dish Soap

Again, how is liquid soap going to work? If poo and TP are stuck to a wall or in a pipe, nothing will get the soapy water in between the stuck object and the wall or pipe.

This fixing method for tanks just isn't a viable option though there are people out there who claim it worked for their camper toilets.

It MIGHT help out a gray water tank to help degrease and do a little tank maintenance, at best.

If their solid waste caused black tank clogs, it needs to be EATEN/LIQUEFIED by something or physically moved by an object such as PEX pipe.

Harsh Chemicals

You might be tempted to use some harsh chemicals in your holding tanks to clear out waste. Again- why?

You risk damaging the seals in the plumbing that keep leaks at bay. Besides, it's best to keep these chemicals out of the dump station or septic tank you're using.

Toilet paper roll on top of RV toilet

Pressure Washing

Using a pressure washer MIGHT work. However, it's much less messy and easier to use some kind of drain snake to puncture through pyramid plugs or RV clogs.

Some claim you may accidentally puncture through your clogged blackwater tank using a pressure sprayer into the toilet, but I don't believe that one.

If your black tank needs a serious cleaning, there are professionals who will pressure wash your holding tanks. This is probably your best option when it comes to pressure washing.

Black Tank Flush

A black water tank flush MIGHT work, but only the wand type flusher.

And only because you have to puncture a hole through the tank's contents if you have a pyramid or a clog, so it could push a blockage through or at least open a hole so you can get drain unclogger product down the tank.

That said if you try to use a backflush method where water is sprayed into the tank through its exit plumbing (your RV's drain pipe you use to dump the tanks), good luck. This won't work.

If you've seen what the inside of a tank looks like when one of these pretty worthless flushes was happening, you'd understand why.

RV Blackwater Tank Clogged FAQs:

Why Does My Black Tank Keep Clogging?

Your black tank keeps clogging for one of a few reasons.

  1. You're not using enough water when you flush.
  2. You're using too much toilet paper, OR you aren't using septic-safe toilet paper.
  3. You have an obstruction in the pipe leading into the tank that keeps catching things on it.

How Do You Snake An RV Black Tank?

To snake an RV black tank, get yourself some PEX pipe. It's flexible so if you have bends in your waste pipe, it will still work.

Plunge through your blockage until you can get water into your tank. Fill it and then use an enzyme treatment to dissolve the plug.

What Do You Do If Your Black Water Tank Won't Drain?

If your black water tank won't drain or flush out, don't panic. You have an obstruction that needs clearing.

Figure out what type of blockage you have first, then follow our directions above to clear out that blockage.

Roll of toilet paper on patio mat

Conclusion

Zero RV owners want their RV black tank clogged. It's bad enough you have to deal with your RV dump hose and your human waste in your travel trailer, 5th wheel, or motorhome.

But worse, having your RV's toilet not working right can cause your camping trip to go very, very wrong. It's a gross and smelly job to fix.

If your black water tank will not drain its waste water, there are three types of clogs you potentially have. A poop pyramid, a pipe clog, or a compacted tank.

Fixing them shouldn't be too hard. Simply figure out which one you have, and then follow the above directions for the type of clog you have, and you are good to go.

Here's hoping this is the last time you have clogging to deal with, as this is a common issue. A blockage only happens to those who don't know how to prevent them!

Now you know how to avoid future clogs.

Kelly Headshot

He-llllo. I'm the co-founder of Camp Addict, which my biz partner and I launched in 2017. I frigging love the RVing lifestyle but in December of 2020, I converted to part-time RV life. Heck, I lived in my travel trailer for over 5.5 years, STRICTLY boondocking for pretty much all of it. Boondocking is a GREAT way to live, but it's not easy. Anyway, I'm passionate about animals, can't stand campgrounds, I hardly ever cook, and I love a good dance party. Currently, I can be found plotting and scheming whether or not to start collecting farm animals (or plotting my next RV trip!) at my beautiful new 'ranch' named 'Hotel Kellyfornia', in Southern Arizona. 

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