Another Black Tank Thread - photos tell the story

I've been a member on RV.net for what seems like eons now. I've read and commented on, probably, hundreds of posts about black and grey tank dumping. I've always been an advocate for flushing the black tank as much as any can. I've commented on how back-flushing from the shower grey water not only helps flush the black tank better, back flushing pulls more "stuff" out when you dump, your black tank does not have to be completely full to dump, back flushing saves water if you do rinse, and if done consistently, tanks never smell.

Yet, in the past, there are still those who claim there is no need to rinse, let alone back-flush their black tanks. They just fill the tank as full as it can get and then dump once and go!

Well, more power to ya! is all I can say. But maybe some photos will help make the "dump once and go" crowd a little more of a believer in taking the time to flush the black tank. For those who never thought of it, let these photos speak for themselves.

First, it's important to have a 3rd valve with clear section of pipe (like a Flush King) so you can see what's actually coming out of the tanks. Second, your system needs to be set up so both black and grey tanks exit the same sewer pipe.

FYI, if you have a black tank flusher on your camper, the black tank flusher will also accomplish the same thing. It just means using more water.

So, here's how it works. The Flush King is valve A, Black Tank is Valve B, Grey tank is Valve C.

1. Open A and B initially and let all the contents of the black tank completely empty.
2. Close A (Flush King), and open C (grey) and let it back flush into B (black). Wait 10 seconds.
3. Close C (Grey)
4. Open A (Flush King) again and let the black tank drain again until nothing comes out any more.
5. Repeat until there is no more grey water left.

So, we use our camper at home all the time. After using the camper for almost a week in the drive way, it was time to prepare for a 3 day weekend, leaving Thursday night last week. I dumped all the tanks at home so I could go the week-end at the camp ground without dumping sooner than needed.

Anyway, here's the results:

I initially flushed and emptied the black tank completely.

After the initial dump, I back flushed the first time. Here's what came out with the 1st Back Flush:

Second Back Flush:

Third Back Flsuh:

Fourth Back Flush, things beginning to look a little bit better here:

Fifth Back Flush:

Sisth Back Flush:

And finally, for comparison, here's the color of the water from the shower grey tank, what remained left.

I normally do not back flush this many times, as I usually don't have that much water in my grey shower tank. This time I did, so decided to get the photos as I went along.

Now, just imagine all the "stuff" that was clinging in the tank after the first dump, if I'd not forced a flush, it would have just sat there. Then the next time, it sits more, and gain, more, and again more, until the tank is ... well ... full of yuck!

This simple technique is so easy to do, it really takes only a few seconds more to back flush the grey to the black (if you only do it one time, it helps tremendously keeping the tanks clean and odor free).

Now, add to this mix the built-in black tank flusher, and (IF) you have the availability to do this, your tank should always be nice and happy.

FYI, I dumped the 5 times using my 32 gallon blue tote, as show in the first photo. So, it's not the amount of water used, it's the backflush itself that cleans thing out.

Well, I've had my rant for the week now.

Seeking Advice

41 Replies

DutchmenSport
Explorer
Sep 19, 2018
One more comment. I normally do not back flush 5 or 6 times. It's usually only once or twice, there again, depending upon how much water is in the grey tank.

Since I had a full grey tank this time, and we were preparing for a trip, I took the time to demonstrate what happens with each backflush and how long it takes to get somewhat clear water flushing out.

Here again, the proof is in the pudding. A single dump does not clean out everything. As demonstrated by the photos, (and by the many, many comments here), there is residue that is left behind after that initial dump. I think that is ALL I was attempting to demonstrate and how much flushing does it take to get it run clear too? (and as demonstrated, it takes a lot of water, no matter how the water gets in the tank.)

To each his own, and once again, there are no right or wrongs when it comes to camping. All we can do is share information and if someone wants to incorporate a new idea they've never thought of before, or tried before, then everyone gains. And not every idea works for everyone either. I'm just information sharing here.
Dutch_12078
Explorer III
Sep 19, 2018
I don't know why anyone would care if the black tank back washes into the grey tank. Pretty much every residence I've ever seen has a single sewer system for both black and grey, and some high end coach conversions also use a single large tank for both. I've used the third valve setup on our RV's for the past dozen or so years, and besides using it for flushing as described, I also use it combine the two tanks at times to extend the grey tank capacity using extra black tank capacity. Works great for extending boondocking time between dumps.
bpounds
Nomad
Sep 18, 2018
I appreciate the time you took to shoot some photos. I often do the same backflushing with gray water thing. Never more than once or twice. I think it is at least as effective as the built-in tank flusher we also have, and I don't have to screw around pulling out a gray hose. My impression is that this does the job of picking up a few solids that dropped out of the stream.

I'm not a fanatic about cleaning the black tank. My opinion is there is no such thing as a clean black tank. The best thing you can do to clean up any solids is to dump immediately after pulling off the highway, while all the stuff is in suspension. Those folks who sit on a site for week after week, might have more concern about build-up. I dump at home now, and try to get right at it as soon as I've parked.

But backwashing with gray is free, and literally takes 2 minutes, and the gray has to be dumped anyway, so why not? Black water will never enter your gray tank if you do this properly, and you would have to really work at doing it wrong to ever get that.
ktmrfs
Explorer II
Sep 18, 2018
I do similar to Dutchman, in fact we have almost identical trailers. but we have a dump station at our house.
(plumbed into the sewer cleanout).

Now we do mostly dry camping, or at best places with water/electric but no sewer. couple that with a week or more at a time, often with daughter SIL, grandkids at places with no dump station. So.... the "use plenty of water" doesn't work!! We need to make the black tank last a week or more, which really isn't that hard if your carefull. But it means lots of solids, and not a huge amount of liquids in the tank.

On the road when I dump, backflush with the grey, finish dumping. At home I use the trailer built in rinser and a setup like dutchman. Only takes a few more minutes to get the majority of gunk out of the black tank. and usually the second rinse results in more TP and poop than the initial dump.

on the way home on our last stop I usually put in dose of HE liquid laundry detergent and scoop of calgon in each tank. Seems to help break up stuff as it sloshes around going down the road. Do this on both black and grey.
ctilsie242
Explorer II
Sep 18, 2018
The best black tank system I've seen was on a custom trailer. It was inside, and had a 12" access port on top, where you could actually go and manually scrape/poke/flush stuff off by hand that was stuck. No guesswork, no backflush... if you wanted it out, you could reach everything in the tank and get it out mechanically.

I have never used a backflush system. I don't see how that is any better than just filling the black tank from the sink or toilet. I also have seen people leaving the backflush system on, with the black tank valve closed, and poop spewing out of the rooftop exhaust vent. This is especially notable on a hot, humid day in the Texas heat.
down_home
Explorer II
Sep 18, 2018
Ours came with a sani flush system and we use it. It takes several minutes to fill the tanks to the top sometimes because we empty them every time we pull up stakes and we clean the tanks. Sometimes if it is just overnight we don't.
It takes a few minutes but who cares. We stay t full hookups almost all the time.
I have encountered some with problems along the way.
Keeping tanks clean prevents problems and keeps sensors clean and working. I don't know how many black tank and some gray tank problems have been discussed here over the years but it is quite a number.
Those who just dump are the ones with prymids, stuck valves and odors in the coach eventually.
We use chemicals too whether sitting still or just pulled up and on the road.
Atone campground in NC Coach behind us hooked up to septic sorta meaning not good connection and opened and left open his black tank the smell was terrible.
Part of it was the septic system was storage and pump out setup and gases coming back out.
The other part was the coach's tanks. When they were getting ready to pull out they had problems. I don't know how long it took them. I offered to help but he didn't want it.
We cleaned tanks and left.
CavemanCharlie
Explorer III
Sep 18, 2018
2gypsies wrote:
Old-Biscuit wrote:
bid_time wrote:
I'm not storing drinking water in my black tank. I don't care how clean it is.
I empty it, Chase it with 5 gallons of water down the commode, good to go.
Simple and quick.

Exactly,......

And in 40 yrs of camping I have YET to have a clogged waste tank or dump line etc.

It's a holding tank and I am going to fill it up with poop again.
My only concern is added water back to black AND Grey so stuff doesn;t stick to bottom of tank.

K.I.S.S. ----is my motto
Least amount of time involved with dump tanks is MORE time relaxing/spitting

Flush/back-flush...have at it if that is what concerns you.
That's why there are so many different ways of doing things.

I'm with you. All these gadgets and additives you guys are adding is unbelieveable!

Me 3.

What are you people eating ????

Maybe a higher fiber diet would help some of you out in a lot of ways.

It should all break down and dissolve rather quickly. If it doesn't you are not using enough water... I guess... Or else, have a salad with every meal. Try eating some vegetables now and then. A glass of Metamucil a day will do wonders for your system,,, and apparently your black tank too.
shum02
Explorer
Sep 17, 2018
bid_time wrote:
I'm not storing drinking water in my black tank. I don't care how clean it is.
I empty it, Chase it with 5 gallons of water down the commode, good to go.
Simple and quick.

I do EXACTLY the same thing, doing it for at least 10 years and never an issue.

I did add a 3rd dump valve though, but more to keep the remote dump valves at bay when they occasionally leak.
WTP-GC
Explorer
Sep 17, 2018
pianotuna wrote:
Hi,

I have a black tank flush installed (OEM). It doesn't always allow the tank level idiot lights to register correctly.

Somewhat on topic:
On my brand new rig, none of the level indication lights work correctly. That's fresh water, grey (1 and 2), black and battery. They worked when I picked it up at the dealership but quit working somewhere between the first and second trip. Since none of them work, I presume it has more to do with the control board than the actual sensors. Nonetheless, I'm in no real hurry to deal with it as I believe those sensors are just what you say...idiot lights.
2edgesword
Explorer
Sep 17, 2018
ScottG wrote:
I read stories about pyramids and other blockages here every week. 30 seconds of my time to flush the tank is cheap ins.

The 30 seconds isn't the issue. The issue is the guy that takes an extra 15 ~ 20 minutes filling, flushing, filling, flush...thinking it has to be done to prevent an issue while a line of people is building behind him waiting to dump.

My educated guess after six years of following a relatively simple and quick process is the person that ends up with a pyramid that results in a problem is the person that hasn't followed the very simple and quick process of having the tank full before dumbing and adding a couple of gallons of water to the black tank after it's dumped. I have absolutely no issue with someone that takes a few extra minutes to use a black tank flush. But the idea that if you don't clean out every last bit of waste every time you dump means you're going to end up with a problem doesn't coincide with my experience or the little bit I know about the physics of dumping a black tank.