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YUCK!! – The Nastiest Part of a RV is Inside the BLACK WATER Tank.

November 10, 2010 by · 10 Comments 


Can you think of anything more unpleasant than a smelly black water tank stinking up your RV?

Well, with  proper care and feeding,  odors from black water tanks need not happen.  Read on to learn how!


Black Water, of course, refers to the discolored, tainted, and smelly water that is discharged from the toilet bowl into a single holding tank.  Please understand that this is a holding tank, not a septic tank.  There is a big difference between the two.

One thing I have learned when a discussion turns to “black water” is that there is little, if any, agreement on what chemical to use in the holding tank to control odors and break down waste.  Nor does everyone believe it is necessary to flush the tank to have it “squeaky clean”.  We DO seem to have a common agreement on how to dump the black tank.

I have been dealing with black water holding tank issues for years.  Now, before I go any further be reminded that with some RV issues the frequency of performing a task does not necessarily make you an expert.  With enough practice, It is extremely easy to get very good at doing the wrong thing!

To begin, lets take a look at what is in the tank (not visually, just from a chemical perspective).

  • Water – just plain tap water from any clean water source
  • Tissue – the material often used to clean the backside of the human body.
  • Solid waste or feces – what I grew up knowing as #2.
  • Liquid waste or urine – what I grew up knowing as #1.

ABSOLUTELY NOTHING ELSE SHOULD BE ALLOWED IN THE TANK – No dental floss, sanitary feminine products, cigarette butts, food, flushable cleaning pads, paper towels, table napkins, chewing gum, cotton balls, or plastic bags containing pet waste.  Nothing but pee, poop, RV rated tissue and water.

OK – you are most likely thinking:  “What about the chemical additive?” and possibly, “Why can’t I put the items Randy just listed in the RV potty – I (may) do it at home?”

It is like this:  They do not dissolve or break down in water; they will remain as solids and can easily become stuck in drainpipe elbows and slide valves.  If you have ever tried to remove an obstruction in a RV holding tank with a plumber’s snake or a section of wire you know it is something you NEVER want to try again.

ALL black water tanks need water – plenty of water – to operate properly.  There is a tendency to empty the tank and then begin using it without adding any water, or only a small amount.  My belief is that you must have at least 25% of your tank capacity as water to begin with.  For a typical 40-gallon black water tank, this translates to 10 gallons of water.

I add 10 gallons of fresh water back into the black tank after I have dumped.  Yes, it goes with me when I leave the dump station and it does add an additional 80 pounds of weight to the RV.  As I drive down the road, it sloshes around in the tank acting just like an agitator in a washing machine.  When I park at home, it sits there and waits for me.

How do I measure 10 gallons?  You can use a bucket filled from the shower or tub faucet.  But, an easier way is simply to run water into the potty for four minutes.  Most all RV water systems are flow limited to 2.5 gallons per minute.

To these 10 gallons of fresh water, I toss in one Cascade Automatic Dishwasher Action Pac before I pull away from the dump station.  The package contains Sodium Carbonate, a water softener also known as “washing soda”; Sodium Silicate, often called “Water Glass” and used as a scrubbing agent; along with a little Dawn detergent, enzymes and perfume.  Together, the Action Pac and 10 gallons of water sloshing around in your tank as you drive down the road will clean the inside of your tank, the surface of your electronic level sensors and help break-up any waste or tissue remaining in your tank.  The solution does have some inherent deodorizing characteristics and WILL NOT kill the good bacteria generated by some holding tank additives.

The next time I arrive at a dump station, which may be days or even weeks if the camper sits at home, I dump the solution and add another 10 gallons of clean water.  To these 10 gallons, I add my holding tank “chemical”.

After years of trying just about every holding tank chemical made, I prefer either the enzyme or bacterial generation additives to the formaldehyde or paraformaldehyde formulations.  Formaldehyde additives attempt to kill all bacteria in the holding tank – thus hoping to eliminate odors.  They may also contain some detergents.  These frequently used chemicals (usually blue in color) are banned in some states and at many campgrounds, since they can quickly destroy the bacteria needed for successful operation of a sewage septic system.  They are the chemical of preference for small self-contained portable toilets and the big outdoor job site or rental toilets.  They can do a good job of keeping odors away in these facilities.  But, there is still the environmental issue to contend with when disposing of formaldehyde based chemical waste.

My personal preference is an additive called ODORLOS.  It promotes the growth of good bacteria that, IMHO, eliminates odors and breaks down waste extremely effectively.  Unfortunately, your tank must be completely free of any formaldehyde or chlorine based chemicals for ODORLOS to work.  Any remaining chemicals from another product will kill the needed bacteria.  This keeps ODORLOS from working, the tank stinks, and people who “try” it are generally disappointed and go back to formaldehyde agents.  Numerous other enzyme and bacterial additives available in liquid, tablet and granular form will work well.  But, all will require a tank free of formaldehyde to work properly.  It may take several dumps and rinses to get the tank clean enough for these chemicals to work properly.

Yet another issue with RV black water tanks is what brand or type of toilet tissue should you use?

The tissue must dissolve or break-up into smaller pieces easily.  We do not want a wad of paper in there that can obstruct drain lines and valves.  Most (but not all) RV toilet tissue is single ply.  I am not convinced this is necessary since we end up using twice as much as we would with 2-ply tissue.

Before using any tissue that is not rated for RV holding tanks, you should conduct this simple test:

Put a sample of your favorite toilet tissue into a plastic bottle, jar, or a glass of plain water with a few drops of liquid detergent.  As a control, put an equal volume of a leading RV tissue into a second jar.

Shake or stir both jars for a few seconds and place them on a table or counter.

Return in approximately two hours and shake or stir both containers again.  When you examine the tissue inside the jar, it should be dissolving into little pieces that fill the jar.  If it is NOT dissolving as well as the “control” jar of RV branded tissue, do not use it in your black tank.

Repeat the test with other brands you like – even those not rated for RV use – to see if they are black tank compatible.

Remember that there are as many opinions on how to maintain an odor free black water tank as there are people owning RVs.  Type the following into bing or black water tanks and you will find literally hundreds of ideas ranging from using bags of ice to clean the tank as you leave a campsite to homemade concoctions to put into the tank.  Weigh each suggestion carefully before adopting the method.

As a summary, these are my recommendations:

  • Use plenty of water – at least 10 gallons
  • Drive your RV with at least 10 gallons of water (25%) in the black tank to help keep it clean.  A cleaning additive such as the Cascade Action Pacs may help this process.
  • ALWAYS keep the black tank drain valve closed when using the RV potty.  Never allow potty waste to enter a dry black tank.  It must have water in the tank.
  • DO NOT put anything in the potty but pee, poop and a readily dissolving tissue.
  • AVOID use of tank chemicals that contain formaldehyde or paraformaldehyde.
  • DO NOT put bleach into a RV holding tank.

Taking these steps will save you a lot of future grief and trouble.  It will also keep your level sensors clean and working properly while reducing or eliminating unpleasant holding tank odors.


11 Responses to “YUCK!! – The Nastiest Part of a RV is Inside the BLACK WATER Tank.”
  1. Patti Faustini says:

    Thank you for your direct comments! It’s helpful when people get to the point ( i.e., #1 and #2) instead of beating around the bush! Patti

  2. Professor95 says:


    That’s EXACTLY what we used to do when we tented camped – Beat Around the Bush with #1 and sometimes #2. :)

  3. Hoby says:

    I agree with your choice of chemical to add to the tank–and was disappointed when Camping World decided to stop carrying that brand; now we have to find another source.

    We have also found that the RV toilet paper from Scott (available at WalMart) is single ply, but more sturdy than most single play brands. Tetford offers a 2-ply version (but it is much more expensive).

    Thanks for the informative post; I like the Cascade idea.

  4. butterbean carpenter says:

    Howdy Professor 9.5,
    Thank you for a very BUNZERESQUE article!!! If it wasn’t for you, Gary and Mark we would all have ‘stinky’ potties… I think I’ll give you 5 stars***** just for the subject matter…

  5. water tanks says:

    Yah…..this is really very great to know how that we can now use the rain water for drinking and for the commercial purposes…But for this I have to install a water filter in my house.

  6. jeff gerod says:

    hello out there, as to black water, we bought a 28ft tt last jan 2010. I purchased a flojet macerator for the tank. I ran the wires to the batteries in the front and pigtailed to plug just above the hose connecto on the trailer. I have several hose ends all are interchangable with radiator clamps and a heavy duty clear hose, I’ve never had a problem yet! I get a clean flush using to back flush hose, neat little system I came up with works great, bought the product from northern tool when they had it on sale. we are heading down to Quartzite for 10 days end of january here’s to great adventures to all a a very happy new year and new palces to explore.

  7. water tanks says:

    Thanks for this as a basic knowledge is provide in it and by reading this most of us takes the necessary steps to avoid it . Storage of water and than utilization of it both things depend and the tank should be cleaned.

  8. joe churella says:

    I have something concerning my fifth wheel black tank. It’s a 2010 Laredo and there is a crack in the tank where the commode 3 inch line goes into the tank. It looks like they forced some fittings together at the factory and caused this problem. Keystone has offered to replace the tank but I do not have much faith in the dealer doing this without causing more problems. Can this three inch long crack be patched or sealed ?

  9. paul payne jr says:

    just a quick tip when you leave your last site and you dump your black water and clean your tank dump a 10lb bag of ice down the comode and add a small amount of water,this will scrubb and clean your tank as you drive down the road then dump it at some point. this will keep your tank good and clean. hope this is helpful . paul payne jr alexander city AL.

  10. Razz says:

    Odd there are so many posts suggesting never use the “blue” waste tank treatment, but the “blue” waste tank treatment outsells every other suggested treatment combined. Wonder why that is?

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