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How To Flush And Clean An RV Black Tank

Now this is a topic that’s on everyone’s mind that owns an RV with a toilet, but one that few want to think about, let alone talk about.  Let’s get down to the nitty gritty dirt on keeping that RV black tank like new and running clean!

Starting with the basics

When at your site with full hookups or when making a needed trip to the dump station, ensure that you drain the black tank first.  Once drained, you then close the black tank valve and open the valve to the gray water in order to empty that tank.  Naturally, the reason for this is to clean the hose or hoses, as the case may be, that are attached from your black and gray water tanks leading into the septic system at the campground.

Once both tanks are empty and valves are closed, go inside your camper and partially fill the black tank again by running some water into the toilet, if you have it available to you.  Also, add some water to the gray tank by turning on your kitchen sink.  You can then open the valves once again in the same order for a bit of assurance the tanks and hose(s) are cleaned out.  If you do not have full hook-ups and must make a trip to the dump station, simply fill a couple gallon water jugs and run them down your toilet and sink as a second rinse.

OK, you know that, right?  And that seems like a no-brainer, right?  Well, it’s only the beginning to keeping an RV black tank, clean, odorless and the monitor system reading accurate – the latter being a common complaint amongst the RV community. Before we go any further, if you are new to the RV world or need a little refresher, here you can find an article we wrote that includes a beginners guide on how to correctly and successfully dump the tanks in a trailer.

Everyone has their theory

Who knew, but there seems to be a hundred opinions of tried and true methods for keeping an RV black tank clean.  Maybe you’ve given a few of these a try or perhaps one or two will pique your interest.

Ice Cubes and Detergent:  The ice cube theory is one that’s been sloshing around for many years.  Some folks simply add 2 to 3 bags of ice cubes into their RV tank and go for a drive.  Many swear by this.  As an added bonus, the theory has been expanded to include adding a quarter cup of dishwashing detergent (NON-antibacterial version) plus 2 gallons of water to the tank along with the ice cubes.

Dawn or Joy seem to get the highest hits for the type detergent to use.  RVers then simply take a drive for 2 to 4 hours, like take one of your excursions for the day, then return to your site and dump and flush repeatedly.  It’s easiest to ensure you do this at a location where you have full hookups.

Add about 3 gallons of water to the toilet when done and the toilet treatment you normally use, take another drive around to mix things thoroughly and then flush the tank once again.

This method may work best with a motorhome since driving around is involved or do it on a day you are relocating your fifth wheel or travel trailer to a new location.  Also, ensure you do not overdo it with detergent or your RV may be foaming all over the place.  This method is used occasionally as a thorough cleaning; it’s not necessary each time you empty the tank, of course.

Yeast and Peroxide Flush:  To get rid of solids and odor in the black tank, try using some yeast and peroxide.  It’s a tried method and an inexpensive one at that.  Add 1 gallon of water to an empty black tank, 4 oz. of yeast and 10 oz. of peroxide.

Take a drive, perhaps to your next camping location, while the water/yeast/peroxide splashes throughout your black tank.  Empty the tank and refill with some water and your normal black tank treatment additive.  This method has been reported to eliminate solids and odor, but not paper.

Calgon, take “it” away:  Another theory that seems to be worth a try is adding a water softener, such as Calgon, to your black and gray water tanks.  This is known as the GEO method although nowhere have I found why it is called this.  In any event, many RVers have tried this method with much success.

Once your tank is empty and valve is closed, mix 2 cups water softener with 1 to 2 gallons of hot water for each tank.  Pour into your sink or shower for the gray tank and into your toilet for the black tank.  The premise is the water softener keeps any gunk from sticking to the insides of your tank and to the sensors.  This should allow the tank sensors to stay squeaky clean, thereby eliminating any crud or slime hanging onto them and causing inaccurate monitor readings.

It is also acceptable to add 1 cup of the original “blue” Dawn dishwashing detergent or 1 cup of eco-friendly laundry detergent to the black tank when you add the hot water and water softener.  This helps to further clean and deodorize the tank.  As an added measure, many RVers include ¼ cup Borax to the black tank along with the detergent.  Borax serves as an excellent cleaning agent.

No driving around this time.  Simply use your tanks as you normally do and empty when the tanks are 2/3 to full.  All these products are safe and eco-friendly.  The GEO method can be used on an “as needed” basis or each time you dump the black water tank.

Tools of the Trade

Perhaps you like using one of the many RV black tank treatments that are on the market, however, still have seen some irregularities in the tank’s reading levels.  We know that can be an irritant playing the guessing game of “when do I dump the tank?”  There are some cool, nifty tools available to successfully clean the RV’s black tank.

Built-in Rinsing System:  Many RVs have their own built-in rinsing system called a black tank flush.  If your coach has this option, it is performed by hooking a separate hose to the black tank flush inlet water valve.  Most manufacturers suggest you leave the black tank valve open while performing the flush to avoid water building up and coming out into your bathroom.

This system is comparable to power washing your black tank to thoroughly clean it.  Refer to your owner’s manual for your personal RV as to how its rinsing system operates.

RV Hydroflush:  The next best thing to a built-in rinsing system appears to be the RV Hydroflush. This works in pretty much the same manner. Depending on the location of your tanks, there is a 45-degree version and a new 90-degree to fit the particular type tank connection.

The Hydroflush is a clear hard plastic piece which will attach to your tank valve.  This allows you to see through it as your tanks are flushing.  Once clear water is continually running out, you’ll know that part of the job is done.

The Hydroflush has a fitting protruding from the bottom portion of it where your garden hose will connect to actually perform the flush.  Once the RV tanks have been emptied, attach the Hydroflush directly to the tank valve; then attach the drainage hose to the bottom fitting on the Hydroflush.  Connect the garden hose to the Hydroflush and start blasting, ensuring your black tank valve is in the open position.

With the Hydroflush, it is suggested you flush the black tank first, but it can also be used on the gray tank once the black tank valve is closed and the gray tank valve has been opened.  The Hydroflush comes with a pre-installed back flow preventer and separate anti-siphon valve to protect the freshwater supply from any contamination.

Tornado Rotary Tank Rinser:  This product truthfully has pros and cons.  The results are similar to any built-in rinse system, but the downside is a rather involved installation.  You’ll have to drill a hole in your black tank to install it.

Reviews range from, best thing yet, to suggestions on making pieces out of brass as opposed to plastic which potentially can break, to it partially cleaned the sensors.  Considering the installation involves drilling a hole in your black tank, properly placing sealant around that hole and then hoping for the best outcome, it seems to me there are better things on the market to try first.

Tank Wands:  Tank wands make life pretty simple.  Flush the black water tank by connecting the tank wand to an outside water hose or via a waterline connected to the bathroom sink which can allow for a hot water power rinse.  If connecting to an outside water hose, you will need to open a window, preferably a bathroom window, to allow the hose to feed into your RV for connecting the tank wand and accessing the toilet.

You then insert the wand through the toilet bowl to power rinse the inside of the tank.  A valve on the handle controls water flow.  Ensure the wand is wiped off when rinsing is completed.  It should be cleaned properly and stored outside the RV considering it’s been diving in your toilet.

There are several brands on the market, such as the Camco RV Flexible or Straight Swivel Stik or the Valterra Master Blaster which are all available on Amazon, ranging from 23” to 42” in length.  You may wish to consider purchasing a tank wand with brass parts to avoid corrosion.

Flexible wands maximize the effectiveness in power cleaning the tank, however, some tanks are located such that they require a straight wand.  Check the location of your black tank prior to making a purchase.  There’s even DIY tank wands to be found online.  Google for whatever best fits your needs if going the wand route.

Tips of the Trade

There’s always some tips and suggestions to make the job a little easier when it comes to the task of cleaning the black tank.  Here’s a few to mull over.

Tank Tips

  • Remember to also clean the “O” ring seals of your gray and black sewer caps.  You can then put a thin coat of grease on the seals to avoid any black or gray water dribbles.
  • After emptying the black tank, always add a bit of water to it.  This keeps the tank and any residue from drying and hardening on the bottom of the tank.
  • Flushing and power washing the black tank is not necessary each and every time.  You’ll find the right schedule essential for your RV.
  • Keep valves closed until you are ready to dump the tanks.  Again, this keeps any solids from drying out inside your tank.  It also keeps odors at bay.  You do not, nor do fellow campers, want to wonder where “that smell” is coming from.
  • Do not dump your tanks until they are at least ½ full.  Keeping enough water in the tanks enables solids to drain out.  You may need to add water to the tanks if you are departing a site and need to empty them, but they are not at least ½ full.
  • This should not need repeating, but never use your fresh water hose for dumping your tanks – EVER!
  • This one I’m repeating – dump the black holding tank first, then the gray tank.  This ensure the hose will be left as clean as possible.  Additionally, run fresh water through the dump hose prior to it being stored.
  • Purchase a clear RV dump elbow for attaching to the tank valve so you can see when waste water looks clear.  Continue running water through the toilet until waste water is cleared.
  • Have a clogged black tank? Well, we wrote an article all about how to clean a clogged tank, which includes a step by step guide. Find the article here.

Important Bonus Tips Pertaining to RV Tanks

  • Buy a box of plastic gloves to wear when performing the deed.  You’ll eliminate any chance of spreading bacteria and can dispose of the gloves prior to getting back into your RV.
  • Supervise children, grandchildren and visitors.  Educate them on the importance of responsibly using an RV toilet.  Nothing should be tossed in the toilet except RV-approved toilet paper.  If your grandchildren have a hay day using the foot pedal flush, you’ll be wondering why you are having to dump the black tank so quickly.  If Auntie Babs decides its an easy place to toss an apple core or peach pit thinking it’s biodegradable, you may be discovering a clog in the line.
  • Additional education comes in handy regarding putting flashlights, cell phones, hair brushes and the like aside prior to using the toilet.  It’s nice to avoid having to fish those sorts of things out of an RV toilet.
  • Never use a campsite’s full hookup to dump toxic waste.  It is rude and environmentally disastrous.  Campers love the great outdoors and use of biodegradable products is the responsible thing to do.  Read cleaning agent labels.  Biodegradables such as baking soda, white vinegar, hydrogen peroxide, organic brands and the like make excellent cleaning products.
  • Keep jars with screw top caps for disposing things later such as cooking grease, alcohol, paints, paint thinner, vehicle fluids, etc.
  • Use appropriate toilet paper.  Yes, it is important.  Naturally there is toilet paper made specifically for marine grade and RV toilets.  Another researched is Scott’s Rapid Dissolve Bath Tissue. It is approved for septic and RV systems.  If you have sensitive skin, Seventh Generation 2-ply is hypoallergenic and can be used in RVs.
  • Do not use colored, thick, perfumed or regular household toilet paper.  It does not biodegrade quickly.  Also, don’t worry about buying expensive RV toilet paper unless you truly like the feel of it.  Cheapo, single-ply, unscented works just fine.
  • Find an RV tank treatment that you feel works best for you.  Many feel the liquids will disperse best throughout the tank and work faster at eliminating and keeping odor down.  You will always want to use a treatment each time after you dump your black tank.
  • RV portable waste tanks, having wheels and a handle to easily transport to the campground dump station, can definitely come in handy at times.  Just remember that it is crucial to sanitize these as well.  Take the same care in cleaning and flushing as you would your RV black tank.


To many one of the most baffling issues in RV maintenance is keeping the tanks of your home on wheels clean and odor-free with precise and accurate monitor readings.  Through trial and error along the way, you will find a solution to go with the flow, so to speak.

No one wants odors permeating through their RV, day or night, and keeping tanks sanitary makes for a healthy, happy camper.  There are many methods and tools out there to flush black tanks and keep them working like they should.  It’s up to you now to determine your fix.

[author title=”About the Author” style=”font-family:lato;”]

Author Nancy Ferri Avatar

Nancy Ferri

Nancy Ferri is recently retired. She and her husband are avid campers who plan to hit the road next year to enjoy some longer adventures throughout the U.S. They also enjoy kayaking, hiking and bicycling in the great outdoors.

7 thoughts on “How To Flush And Clean An RV Black Tank

  1. No matter whether you’re replacing your previous toilet or installing a new one in your new house, it’s important to realize the advantages and shortcomings of different kinds of toilets. Dual flush toilets are extremely effective means of flushing your toilet and conserving water at the exact moment.

  2. Fuel injector cleaners are a mixture of complex chemicals, most of them solvents that can easily clean deposits.

  3. When I initially commented I clicked the “Notify me when new comments are added” checkbox and now each time a comment is added I get several e-mails with the same comment. Is there any way you can remove me from that service? Thank you!

  4. We were told to use Borax, along with Calgon and Dawn. I noticed that the borax doesn’t break up very well…and wondered if you have ever heard of it clogging the holding tanks by solidifying? Should we just stick to powdered Calgon and Dawn?

    1. Dissolve the Borax in a gallon of hot water in a bucket or big pot, then pour it in the toilet with Calgon and Dawn.

    2. We have been using borax and dawn dish soap. We put the dawn and borax in a gallon of water, mix well. Then let sit overnight and shake again. It all seems to dissolve after sitting in the water overnight.

  5. Hello, I was wondering if you had any tips or tricks for cleaning the neck area of the toilet itself. We recently became full time rv-ers and I’m noticing a build up in the toilet neck, going down the shoot.

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