Dumping & Cleaning an RV Black Tank

TheRVgeeks Maintenance, Water & Sewer 14 Comments


We demonstrate how to dump RV waste water holding tanks and thoroughly clean the black tank. Keeping your sewage tank super clean requires following a few simple procedures which will make it stay odor-free.

To view our “express” version of this procedure watch:

RV Holding Tank Dumping 1-2-3

Lots of RVers think their black tank is clean when they just empty it and flush out the sewer hose with water from the grey tank.

Even those RVers who use a black tank flush system often don’t utilize the most important piece of equipment necessary to monitor the cleanliness of the black tank: a clear sewer elbow.

And even using a clear sewer elbow on your camper isn’t enough. As we demonstrate, using a black tank flush connection, and plenty of water STILL won’t do the job. Using the proper technique is essential for maintaining the black tank and keeping it clean and odor-free.

We go through the step-by-step instructions for making sure that your RV holding tanks stay clean and fresh, making your motorhome, travel trailer or fifth wheel a nicer place to be.

We’ll also cover a few basics about sewer connections, flush valve use, toilet chemicals and special techniques for cleaning and deodorizing a problem sewage holding tank. In addition, we’ll review some details that every RVer should know about when and where to empty their black tank.


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We're handy RVers, not professional technicians. We're happy with the techniques and products we use, but be sure to confirm that all methods and materials you use are compatible with your equipment and abilities. Regardless of what we recommend, consult a professional if you're unsure about working on your RV. Any task you perform or product you purchase based on any information we provide is strictly at your own risk.

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Comments 14

  1. What is the water softener that you are referring to about cleaning the black tank? Is it water softener salt?
    Thanks, Kristen

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  2. This is an awesome video. I knew what you was going to do before you did it when you reached down and closed the drain valve while the tank flush was still spraying water into the tank. I learned that one on my own. One day while draining my tank, I thought to myself, ” If I closed the drain valve and let the water spray into the tank, It would ad water and stir things around. Well I was right. It sure did and there was more brown stuff came from the drain. I do use the clear elbow so I can see whats going on while dealing with this situation. I’ve been full timing sense I was in my teens, and I’m now 62, so I’ve learned a few things over the years… So, Thanks for helping others learn the proper way to drain and clean their black tanks. Thumbs UP !

  3. I wonder if you could help us please, we have a Newmarket Dutchstar, we have tried to flush our black tank but the water is spraying out over the fresh water tank from a small pipe is sticking up by the toilet waste pipe underneath where the black tank is and this is where the water is spraying out. Do you know how we can fix this problem. We have managed to take a photo of this if it would help. Many thanks

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  4. Pingback: Tips for Storing Your RV When You Need to Leave it Behind | Technomadia

  5. Hello! I’m fairly new to RV’ing and still learning quite a bit. First I want to thank you guys for all the informative videos you post. I came across your account via Gone with the Wynns. Watching these videos definitely helped with my first RV purchase.

    My RV is a 2004 Damon Challenger 348. Not sure if this is a issue or not but I’ve noticed the valve to flush out the black water tank leaks. A fellow RV’er told me that this is normal to prevent overflow. My concern is, based on the leaking flush valve, I have to empty my black water tank in less than a week. It will start to smell and I can see a slow drip coming from the sewage bay area. I’m a single mom of four kids including a set of 1yr old twins; so only three of us use the toilet. I remember you saying you can go two weeks before dumping your black tank. My tank is approx. 50gal, so I find it odd that the leak is from overflow in less than a week. When I connect my hose to the valve to flush out the tank it doesn’t leak at all. Something else I notice is when I dump the black tank I can tell by the amount that comes out that it is no where near 50gal worth of waste.

    Not sure if this matters but we currently use the RV toilet for #1 only and we don’t flush toilet paper. I have a DIY composting toilet for #2. The leak will start approx. 4-5 days after I dump.

    Looking forward to hearing back from you soon. Thanks for your help in advance!!

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      Hi Tamyka. First, we have a couple of questions to be sure we understand exactly what’s happening.

      1. Is the leak coming out of the fitting where you attach a fresh water hose for the purpose of flushing the black tank? (see next question for more clarification on WHAT is leaking out)
      2. Can you tell if the leaking water is fresh water or waste water? If it’s FRESH water, it could just be the left-over water from the last flushing you performed… the backflow prevention valve may be allowing that fresh water to leak back out. If it’s BLACK water leaking out… you need to get that tank flusher repaired/replaced!
      3. Is this a factory-installed tank flushing system, or an aftermarket one? Either way, it should have a backflow prevention device that keeps ANYTHING from coming OUT of the black tank! (see previous question)
      4. When you dump the tank, are you doing it because the tank sensor shows full? The problem could be that it shows full when the tank is only partially full. That would account for both the tank seeming to fill too quickly and not much coming out when you dump it.
      5. Does your tank sensor read empty after dumping? If not, then your tank sensors are either clogged/blocked (in which case you’ll need to do a thorough cleaning of the tank to get them cleaned) or not working correctly. Our guess is that your sensor is incorrectly indicating full, but that would of course not account for the odor or the leaking.
      6. Can we assume that you do not keep the flushing hose attached except when you’re flushing, so that there’s no way any water could be leaking in through the hose? If you are leaving the hose attached, try disconnecting it to be sure that’s not the source of any leak.
      7. When you say that there’s an odor… is it coming from the water bay where the liquid is leaking from the flush valve? Or is the odor INSIDE the RV? If it’s in the water bay, that may be the indicator that the liquid leaking out is waste water… which means that flush valve should be repaired/replaced. If it’s INSIDE the RV, when do you smell it?

      We can only go 2-3 weeks without dumping when we’re staying in campgrounds with bathroom facilities, allowing us to avoid using our own bathroom as often. When we’re boondocking with no other facilities available except our own, it’s more typical for us to have to dump our 45-gallon black tank more often, maybe every 1-2 weeks.

      1. Hi guys! Thanks for the quick response.

        1. Yes, it is coming from the fitting for flushing the black tank.

        2. It is definitely waste water.

        3. It is a factory installed flushing system.

        4. I dump the tank once I start to smell the odor and visually see a slow drip coming from the sewage bay . The sensor light will kind of show 2/3 full. I say kind of because the sensor light for 2/3 goes on and off, especially if the kids are bouncing around. The 1/3 light stays steady. I’ve never reached full.

        5. After I dump the sensor shows empty.

        6. I do not leave the flush hose attached.

        7. The odor comes from the sewage bay where the leak is present. Sometimes I smell the odor outside first and by the next day I will get whiffs of it inside the RV right above the sewage bay area which is right outside the bathroom door in the hallway. At that point I go and dump. After I dump there is no odor present from inside or out.

        Sounds like I need to repair/replace the flush valve. Is this something that could be done without taking it in to a professional? If I do have to take it in is it better for me to buy the part myself? Also, if you have a ball park figure of what a repair like this should cost please let me know. I know for a fact I’m an easy target. :/

        Thanks again for all your help! :)

      2. I thought I should mention one more thing. When I open the door to the sewage bay there is a small puddle of waste water inside.

        This past week I dumped extra early due to having company. So we only went about 3 days after the previous dump. There was no leak or any waste water in the bay area. That pretty much let me know once the waste water reaches the flush valve which is not that high on the black tank it starts leaking.

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          Thanks for all the detailed information, Tamyka. From what you’re describing, it sounds like the vacuum breaker (which is designed to prevent liquid in the black tank from being able to come out through the water inlet for the flushing port) has failed. In and of itself, the vacuum breaker is not a particularly expensive part (approx $20 online). But the level of difficulty for replacing it, and the associated cost if a professional is doing it, will depend on WHERE the vacuum breaker is installed (i.e. how easy it is to get to).

          If you feel comfortable trying to tackle the job, you could start (after being sure the tank has been dumped) by tracing the water line from the inlet port where you hook up the flushing hose. That should have plumbing behind it that probably goes up (usually above the level of the black tank, so it could be fairly high) to a vacuum breaker. Another hose will go from the vacuum breaker back down to the sidewall of the black tank where the rinsing unit itself is mounted. If you can easily remove the vacuum breaker, you could take it to a local RV repair facility and they will most likely have a replacement (or you could look for a similar unit online… like this one on Amazon). You may want to use a ziploc bag and a rubber band to cover over the hose that comes from the black tank to the vacuum breaker if you remove it… and be sure to keep that hose up above the level of the black tank so that it doesn’t “ooze” anything! And, obviously, you should refrain from using the toilet while this part is removed… JUST to be safe! ;)

          If you’re not comfortable tackling the job yourself, you could ask around at the RV park you’re in to see if anyone knows of a local mobile RV repair service. There are lots of them around the country… and they are very convenient, since you don’t have to move the RV to take it in to the service facility.

          Hope this helps!

      3. I am noticing a horrible odor from my black tank. I live in my RV so it never moves. I’ve tried several of the additives. Today is particularly bad.
        What can I do. I don’t see a tank flushing system on the outside. I have a Mallard M325.

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          Oh boy, Carol. Sorry to hear you’re having an odor problem. There are a couple of things it could be… and a couple of things you could try.

          First off, it’s possible that, since you’re stationary, bees/wasps/spiders have built nests in your black tank’s vent pipe (or pipes… sometimes there’s more than one), which would prevent odor from being able to vent to the roof. So you may have to remove the vent cap and carefully try cleaning the vent tube to ensure there’s a clear path for air (of course being careful not to get stung if it IS bees!)!

          Also, since you’re stationary, it’s possible that you need to do a more heavy-duty cleaning of the tank. Lots of the tank additives don’t do much other than try to mask the odor with nicer-smelling odors. So you may want to try something like Happy Camper’s Extreme to “eat out” the “gunk” that may have accumulated. It might take a couple of soaking treatments to get all of the accumulation from the bottom & sides of the tank eliminated.

          Since you don’t have a tank flushing system, you could try using a wand like this Camco Swivel Stik that you can put down the open toilet in order to help “blast” loose any accumulated “stuff” in the tank after you dump. We haven’t used one of these (since we have a built-in tank rinsing system), so we’re not sure how effective it would be.

          Lastly, if you’ve tried/checked everything else and you’re still having a problem, you could try installing a 360 Siphon Vent on your black tank vent pipe on the roof. These are much more effective at creating suction up the vent stack, so that gases and smells don’t find their way into your RV.

          Hopefully, one (or more) of these will help you to get rid of the odor!

  6. I just use Borax in my tanks. After dumping them I refresh them again with borax. Never have had a odor problem. Lots of rinsing before storage and I leave about 3 gallons of fresh water with borax in my tanks when in storage.

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