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Black tank science

Turtle_n_Peeps
Explorer
Explorer
Lets talk about the science of poo. It’s important to know the science of poo to know what happens to poo in your RV. This will be a long read even though I will try my best to keep the length down to a minimum.(didn't happen) 😞

I have seen some wild claims on this site so lets take a look at a few shall we.

“My poo don’t stink.” Sorry, but it does. It really does! Bear poo, camel poo, dog poo, cat poo and even people poo; it all stinks! Why? Because of that pesky little unicellular microorganism called bacteria. You see, when living they emit gases. Most of them smell really bad! You have good bacteria and bad bacteria in your gut. All bacteria produce gases. If you have a diet high in sugar, (and who doesn’t now days!) it can make your poo smell really bad! Eat things high in sulphur will also cause you to have a real stinky stool. Really makes no difference, because all poo smells no matter what some members of RV.net say.

So why do people on here claim their poo “don’t stink?” Well; a few reasons I can think of. One of the biggest is losing the sense of smell with age. We lose a lot of things with age and one of them is the sense of smell! If you are older than 60 you have lost a lot of your sense of smell according to the Mayo Clinic. Do you smoke? If so, you have lost a lot of your sense of smell. Smoking damages the olfactory nerves in your nose and when this happens you lost a lot of your sense of smell. For those of you that have smoked and quit you know what I’m talking about. Now that steak or that chicken tastes soooooo much better doesn’t it!

“The pressure of poo.” Another reason is pressure, or lack thereof. You see, when you flush your RV toilet you are directly exposed to the contents of your holding tank. Unlike your home toilet, your RV toilet does not have an air lock. So when you open that toilet trap door the gases have two ways to go. They can come up and waft all over your RV or they can be held down by positive pressure in your RV and go out the roof vent. What is this talk about positive pressure? You see, your RV might have a slight negative pressure and your holding tank might have a slight positive pressure. That is bad because gases, much like electricity, they like to take the easy path, and in this case the easy path is to the negative pressure inside of your RV when you flush. This is the reason you really should not run your overhead fan when you flush your toilet. If you do, you are creating a negative pressure and drawing that sewer gas out of the holding tank into your RV. Ya, not good! Kind of like being in meeting room all day long for a bean convention…….but worse!

“Heat, cold and bacteria.” Much like us, heat and cold can effect how lively bacteria is. “Most” bacteria does not do well when it’s cold. Hence the reason we refrigerate our food. Bacteria does very well when it’s warm or even hot. So if you RV in cold areas more than likely you won’t have much of an odor problem with your poo. Because of work, I typically RV during summer months. This being the case, most of the places I RV in and when I RV are in the 90’s or even the 100’s. This can be a big problem with odor! Ever wonder why you can smell that city sewage treatment plant on the hottest days of summer and not in the winter? Well this is the reason why! Ever wonder why most hospitals are kept cold? See above. Now you know!

“The concrete myth.” I’ve seen many time on here that poo can turn to “concrete” in your tank. They don’t mean it literally can turn to concrete, but that it can get very hard. No, not really. This is ridiculous! You see, poo is a water soluble organic material. If it dries out and gets hard, you can just add water and wala, you have a poo shake again! It really is that easy! When traveling, your black tank is having a literal aaaaaaaaaaaa “# storm “ inside of it. Sloshing and banging, back and forth and up and down. Kind of like a poo blender if you will. Believe me on this, if you have a tank with hard poo in it, all it will take is some water and a little time and some agitation and will turn right back into a poo shake again!

“Water will stop the poo smell.” Aaaaaa, no it won’t. If this were the case, embalmers would use water in mortuaries instead of formaldehyde. If this were the case sewer plants would not smell! Not to say that water is bad; not at all. Water is good! And water is very good in your black tank! Water can dilute the poo and that is a very good thing for several reasons! The more water to fecal mater you have the “less” concentrated the poo will be and the “less” the smell will be. Notice I used the word “less”, and not all. On hot days it won’t do hardly a thing for the smell in your black tank. Remember that the bacteria that is in your black tank is making it smell so bad. Water won’t kill it. As a matter of a fact, bacteria loves moist, damp and wet areas!

“Chemicals.” Oh boy, here we go! Let me begin by saying water does not kill the bacteria that causes black tanks to smell; “some” chemicals do. < Read that again! Now read it one more time! Stomp your feet, jump up and down, cry, snivel and whine; it’s true whether you like it or not. The real question is do “you” need chemicals? I can’t say? You might be a smoker and over the age of 70 and you can’t smell hardly anything. In that case, I would say no, it’s a waste of money. You might have a positive pressure in your trailer at all times and when you flush, hardly any gas comes out. If that’s the case, I would say no and a waste of money. If you camp when it is cold and your black tank stays cold, I would say it’s a waste of money. For “me” I have to have chemicals in my tank. Ok; not have to have to have;………. but let’s say it’s very unpleasant in my trailer when I flush my toilet without chemicals in the tank!
What do those chemicals do anyway? Well, that depends. Some RV black tank chemicals are nothing more than perfumes. IMHO they are not good. What will happen is your poo will have a pine scent smell or a lemon unfresh smell! Looking on the bottle “I” use, it says the major ingredient is formaldehyde. And why do morticians use formaldehyde? To KILL bacteria! And dead bacteria does not gas off like live bacteria do. Hence the reason dry poo doesn’t really smell that bad. When poo is dry, all (most) of the bacteria is dead; and dead bacteria does not have much of a smell; at least compared to live bacteria!

If you want to kill the smell in your black tank you NEED to KILL the bacteria. No if’s and’s or “butt’s” about it!

I hope you had a great time learning about the science of poo and how to mitigate the smell of it in your RV. Happy RV’ing!
~ Too many freaks & not enough circuses ~


"Life is not tried ~ it is merely survived ~ if you're standing
outside the fire"

"The best way to get a bad law repealed is to enforce it strictly."- Abraham Lincoln
33 REPLIES 33

Turtle_n_Peeps
Explorer
Explorer
OFDPOS wrote:
Since speaking from personal experience being a turd herder for 6 years.
Worked for a City in the Sewer Dept.

Rich snobs poop smells just as bad as the poor folk's poop living on the other side of the tracks ! lol

Only difference the rich snobs poop has more fiber holding the poop together ...
Oh and just as many syringe needles !
Even just as much cat litter and egg shells we flushed out of the lines too.

Never understood why people put their egg shells in the sink and garbage disposal . They clog up lines , they don't disintegrate just stay that small size until they go through the Sewer plant and out to the drying beds then finally slowly dissolve would be a term to use ?..


Thank you for your voice of experience! My good friend is in the water treatment business and he calls is "lumpy water."

I find it very amusing the amount of people (even on this thread) that try to imply their $@$^ don't stink. They want to talk about anaerobic and aerobic like it makes a difference in this discussion. Look people, your "holding tank" is not a waste water treatment plant so stop acting as if it is. There is no oxygenators or treatment systems in your holding tank. So stop posting pictures of a septic tank and talking about treatment plants.

The fact is your $#%t stinks right as it comes out of your body. IT STINKS! If you deny that; you have one of the problems I mentioned in the first post.
~ Too many freaks & not enough circuses ~


"Life is not tried ~ it is merely survived ~ if you're standing
outside the fire"

"The best way to get a bad law repealed is to enforce it strictly."- Abraham Lincoln

OFDPOS
Explorer
Explorer
Since speaking from personal experience being a turd herder for 6 years.
Worked for a City in the Sewer Dept.

Rich snobs poop smells just as bad as the poor folk's poop living on the other side of the tracks ! lol

Only difference the rich snobs poop has more fiber holding the poop together ...
Oh and just as many syringe needles !
Even just as much cat litter and egg shells we flushed out of the lines too.

Never understood why people put their egg shells in the sink and garbage disposal . They clog up lines , they don't disintegrate just stay that small size until they go through the Sewer plant and out to the drying beds then finally slowly dissolve would be a term to use ?..

campigloo
Explorer
Explorer
Hats off to ya turtle. This is by far the most fun post I’ve ever seen on this subject.

Ralph_Cramden
Explorer II
Explorer II
myredracer wrote:
If you're getting bad odors, it could be a sign that you're not adequately flushing your tank and "stuff" is getting left behind.


Or it could be a result of eating way too much cheese......or cabbage!
Too many geezers, self appointed moderators, experts, and disappearing posts for me. Enjoy. How many times can the same thing be rehashed over and over?

myredracer
Explorer II
Explorer II
There is no need to kill the bacteria and you shouldn't anyway, especially if dumping into an on-site septic disposal system, which need the bacteria for digestion in an in-ground holding tanks. Dumping formaldehyde into a septic system can cause it to fail.

As above, effluent has aerobic (oxygen "loving") and anaerobic (oxygen "hating") bacteria in it. The aerobic bacteria begins the effluent digestion quickly whereas the anaerobic bacteria takes weeks. It's the anaerobic bacteria that creates the smelly rotten egg odor, not the aerobic bacteria which creates a faint musky smell.

A traditional sewage holding tank looks like in the photo. Heavy solids sink to the bottom where anaerobic bacteria live and scum floats to the top where the aerobic bacteria live. The majority of digestion occurs in the scum layer. Newer "technology" pumps oxygen into the effluent in a holding tank (residential) and mixes it into the solids up for more efficient and faster digestion by aerobic bacteria.

An RV holding tank is simply waaay too small to allow for solids sinking to the bottom and a floating scum layer plus the solids are normally never in there long enough for anaerobic bacteria to create the smelly odors.

I challenge anyone to find an engineer or other professional in the field of sewage disposal system design or gov't agency that would say you should kill bacteria in any holding tank. The State of California for example, outlines why not to use formaldehyde in RV holding tanks here.

Plenty of water is the answer for RV holding tanks. Works great for us. If you're getting bad odors, it could be a sign that you're not adequately flushing your tank and "stuff" is getting left behind. But then, some folks freak out by the slightest whiff of a tank odor no matter what.

Ralph_Cramden
Explorer II
Explorer II
RayJayco wrote:
I thought California banned the use of formaldehyde in RV tanks back in 2009... :h


Probably so, it seems Califorinia bans, or at least tries to ban just about everything, including common sense. :B
Too many geezers, self appointed moderators, experts, and disappearing posts for me. Enjoy. How many times can the same thing be rehashed over and over?

time2roll
Explorer II
Explorer II

RayJayco
Explorer
Explorer
I thought California banned the use of formaldehyde in RV tanks back in 2009... :h

I know that I wouldn't want to dump it in a septic tank system, although they say the tank can rebound in a few days...
Inquiring minds want to know...

wa8yxm
Explorer III
Explorer III
I believe with frequend "Dumps" the bacteria do not have time to grow all that much.. And there are two types of bacteria Aerobic and anaerobic The first type can indeed live in your black tank (It means they like an oxygen rich (Air Supplied) enviorment) the second (no air) live under ground. Those are very very stinky. The only time I've had a noticable Stink issue is when I leave a dump valve open so the Anaerobic bacteria gasses back up the pipe.

But I flush often

IF I'm going to be more than 2 weeks w/o a dump.. I do have a chemical (Well Biological) I add.
Home was where I park it. but alas the.
2005 Damon Intruder 377 Alas declared a total loss
after a semi "nicked" it. Still have the radios
Kenwood TS-2000, ICOM ID-5100, ID-51A+2, ID-880 REF030C most times

suprz
Explorer
Explorer
Ive also seen you tube videos and read about "struvites" which are crystals that form in the black tank from the gasses drying and clinging to the walls of the tank. Kind of looks like the rocks that have crystals growing inside if them can't remenber the name... Geodes?
Proud father of a US Marine

T18skyguy
Explorer
Explorer
" The older I get, the more sensitive my nose is getting! Strange as that may sound, but my "honker" seems to have become extremely sensitive in the last few years."

Same here Dutch. I think they should call it Hound dog syndrome. I get severe migraines from smells, perfumes, cigarette smoke, but I've had this many years since my forties and it's only gotten worse. When my niece visits with her new born baby, the instant she pee's her diaper, I smell it and inform her, even if she's in another room. I'm the first in the neighborhood to smell a wildfire. By and large it's a curse. I wish other parts of my body worked as well as my nose 🙂
Retired Anesthetist. LTP. Pilot with mechanic/inspection ratings. Between rigs right now.. Wife and daughter. Four cats which we must obey.

valhalla360
Nomad II
Nomad II
Turtle n Peeps wrote:

If that were the case septic tank pumpers would have a hell of a job! They open the lid, stick the hose in and pump. Least that's the way they did mine.


Septic pumpers have powerful suction hoses. RV waste is a wide flat bottomed tank drained by gravity.

So while the solids that wind up on the bottom may not be real touch to dislodge, the draining of an RV tank is so poor (relatively) that once the layer forms, you don't have enough agitation to dislodge it.

Letting it dry onto the sides...that a different ballgame. That will make it difficult to remove...sure it will rehydrate but it will then still be stuck to the sides.
Tammy & Mike
Ford F250 V10
2021 Gray Wolf
Gemini Catamaran 34'
Full Time spliting time between boat and RV

2edgesword
Explorer
Explorer
Regarding material hardening if you allow the black tank to remain dry. The comment that poop will rehydrate doesn’t deal with the issue. Its not just poop in the tank but a mixture of poop and paper. If that mixture is allowed to dry it will harden like concrete and may not easily rehydrate to the point where it can be easily flushed from the tank.

Not applicable
DutchmenSport wrote:


But I do have to disagree on one thing: The older I get, the more sensitive my nose is getting! Strange as that may sound, but my "honker" seems to have become extremely sensitive in the last few years. I'm 63, never smoked and my "honker" picks up smells and odors that most others never notice or can't smell. For example, when we pulled up to the campsite we are currently at, I stepped out of the truck, walked past the fire pit and smelled cigarettes. (yes,.... really!)...I looked down and sure enough, a dozen or more cigarette butts. My nose drive my wife nuts.





I have the same issue, my sight and hearing are getting very bad, but I can't stand how stinking good my sense of smell is. I can even get the gag reflex if I'm not careful.


As for the OP doing a study on Poo? I think I'll just stick to researching routes and things like that, I don't want to "step in anything" I'll regret.... and I read the entire posts, what's wrong with me.

P.S. why don't they add a "water-trap" like residential potties? Wouldn't that help in smells when opening flap to release? Not enough water and pressure to force the stuff down?

Normy
Me
DW
DS
DS
Oscar
Buddyboy