Clearing a clogged RV black tank with chemicals

The tip below was inspired by a discussion on the RV Basics Yahoo group. A member of the group wrote that he was advised to keep his RV black tank valve open during the winter to avoid freezing. The result of following that ‘tip’ was a clogged black tank.

I have to say that while I invaribly believe what I write… I don’t offer tips I wouldn’t follow myself. Several members of the group have passionately disagreed with me. I offer my opinions as food for thought. It’s up to you to decide what will work for you. Please feel free to add your comments below.

While I believe the mechanical methods: broomstick or awning wand down the toilet, toilet flush wands, back flushing, etc. for clearing a clogged black tank are usually the most efficient and cheapest, I see no problem with using chemicals if one wants to do so.

I’ve never agreed with those who caution against using Drano, Liquid Plumber, etc. in RV plumbing because it will harm something in the system.

Here’s why.

RVs are plumbed using mostly the same plastic piping and fittings that houses are plumbed with. Even the ‘special RV’ plumbing fittings and parts are made from the same plastics. So if household plumbing chemicals are safe to use in household plumbing I cannot see why they are not safe for RV plumbing.

The only ‘seals’ in my RV’s plumbing are in the dump valves and they appear to be rubber. I have not found any evidence that plumbing chemicals have a harmful affect on rubber. Even if there is, I can’t believe that short term exposure during the unclogging of a black tank would be a problem. Rubber is pretty tough stuff and will be rinsed well with water after the project is complete.

As for these chemicals killing off waste digesting micro organisms, the Drano company website says their products are not harmful to septic systems. Okay, so it was the company saying that. I have to believe the FTC or an enterprising lawyer would have taken action already if it could be proven otherwise.

Keep in mind we are discussing how to clear a clogged black tank. We’re not talking about using these sludge busting chemicals on a regular basis. Once the tank is cleared, rinsed and ready for service again you can introduce new enzymes and bacteria back into the tank if you want to.

Then again, I don’t consider my black tank to be a mini septic system. It is simply a holding tank to store the waste until it can be properly disposed of. Therefore I see no value in costly enzyme tank additives.

To help prevent future clogs always keep the black tank valve closed. Don’t empty the tank until it is at least 2/3 full. If it isn’t 2/3 full, add water until it is. After each dump and rinse, close the valve and add enough water to cover the bottom of the tank. The first few times you flush solids use extra water to flush the solids away from under the toilet. As the tank fills you can use less water to flush to increase the time between dumps.


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16 Responses to "Clearing a clogged RV black tank with chemicals"

  1. If you feel you need to add a “digester” to your Black Water tank,just add one pack of bakers yeast (can be purchased at the Grocery store) to the tank, It will break up the solids into liquids. It is all natural!!

  2. I bought an older RV and I am beginning to believe it wasn’t dumped and over time the liquids evaporated and it has turned very hard. I do not have a sewer hook-up. Do you have any suggestions for breaking this up? Also, advice on a macerator?

  3. We ended up having the dreadful clogged black tank. After some research on the internet, we came down to the following options: take our 5th wheel to a RV service shop, call a plumber, run a snake through the plumbing, or try to use Drano. The first option was basically not going to happen seeing the nearest RV service shop was hundreds of miles away, and they would charge an arm and a leg for their service. The second option, the nearest plumber is 1/2 hour away, and they would still charge an arm and a leg, especially for something we could do ourselves. Well, we opted for the fourth option, drano, keeping in mind if that didn’t work we were going to try the third option of running a snake through the plumbing ourselves. Went down to the local grocery store and bought a bottle of Drano for $4. A half hour after pouring it down the toilet, voila, the blank tank was unclogged! Of course, we took your advice and just made sure we rinsed out the tank very well and dumped it again. We just wanted to say thank you for your reasoning on rv plumbing vs. home plumbing, and also for saving us a a few hundred dollars and a long road trip!

  4. We had both tanks black and gray hydro cleaned 1 1/2 years ago, the tech suggested no chemicals in anymore which is how we’ve rolled since then. I relish the comments about Drano and Liquid Plumber though as I’ve noticed that my kitchen sinks and shower drain very slow even after all my efforts for no grease, dawn dish cleaners etc. Thank you for the info. And to any interested person re hydro cleanse.. go for it the best money we’ve spent

  5. Thank you for all the helpful hints. My husband & I are new to RV camping. (Tent & pop up camped we done in younger days). In our Senior years we decided to RV camp. I’ve researched “how to do things on Internet. Out of all of them. Your site is the most easy to follow & understanding. We greatly Appreciate; all advice in your post. Even, if it doesn’t pertain to any problems at the time. I keep a note book at hand; Jotting down for later use. Once again THANK YOU. From our newly RV skills to Your Season Skills HAVE A GREAT DAY.

  6. I have no information that those products will work but I also have no information that they will not. Before you try them, consider where you will be dumping the tanks after treatment. If you will be dumping into a septic system you’ll want to use a septic system safe chemical. If You do try them be sure to let us know the results.

  7. I bought an older camper and no matter what kind of Rv/Camper treatment I use in my black water tank it still gets clogged. I leave the valve closed at all times except when dumping but once finished I close the valve. I’ve started putting all toilet paper in a small trash can with a bag. For whatever reason my number 2 solid gets stuck in the pipe connected to the tank. I’m constantly using a wand to push it down. The treatment I buy along with water by passes on down. Do I not have enough water pressure? How can I fix this? Has anyone else had this problem? This isn’t just a camper to me, it’s home. My home! Thank You for your time, God bless!

  8. To help prevent future black tank clogs always keep the black tank valve closed. Don’t empty the tank until it is at least 2/3 full. If it isn’t 2/3 full, add water until it is. After each dump and rinse, close the valve and add enough water to cover the bottom of the tank. The first few times you flush solids use extra water to flush the solids away from under the toilet. As the tank fills you can use less water to flush to increase the time between dumps.

    To help clear solids from the toilet, add water to the bowl before you do your business. You can add water to the bowl by depressing the foot valve just enough to start water running into the bowl but not open the flush valve. But let’s face gorilla in the room, there are going to be times when a lunker is going to get stuck crosswise and not get flushed down. In that case, you’ll have to resort to manual methods.

  9. Linda Kuppenbender · Edit

    I have a 1983 rv i have been trying for 3 days to unplug my toilet,. Today i tried to use a rod to push the waste down, i got some but the water i dump in to take the waste to the black water tank just passes around the waste, when i get paid i will try draino to see if i can unplug it, my kitchen sinks are plugged now too. Are yhey related to each othere?

  10. The two article I have posted(links below) offer my best advice. Maybe others will post some suggestions in the comments. Generally, the toilet – black tank and the kitchen/shower -gray tank are separate and are not connected except at the main dump valve.

    Once you manage to get the tanks unclogged, be sure you follow the guidelines in the article linked below.

  11. My black water and gray water tanks are both plumbed into a septic system. My toilet is clogged up both my black and grey tanks valves are open at all the time but he black is clogged up is there anything I can use such as liquid fire

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