I think I have an idea now after reading through old posts how this works. I like the idea of flushing gray water through the black water tank to help flush it out.
But it seems that if the third valve is closed after emptying the black water tank and with the black water tank valve is still open and the gray water tank valve is opened, gray water will back up into the black water tank until some equilibrium is reached or a disater occurs.
Then what? Close the gray water tank valve and open the third valve and drain the black water tank, then close the black water tank valve and open the gray water tank valve and drain the rest of the gray water.
The possibility of getting black water stuff backed into the gray water tank bothers me. It seems like they should be kept separate.
Is there a check valve in the gray water waste line ahead of the gray water valve to prevent backflow?
Since the gray water tank is almost twice the size of the black water tank isn't there a chance of a black water tank overfill (overflow). Ugh!
It seems like it would be nice to have the option of emptying the gray water tank directly or routing it through the black water tank in series (after it has been emptied) to flush it out.
So from those who have done this mod to one who is thinking about it, how does it work? Any problems? Did you domit differently than I am imagining?
Maybe a diagram would be helpful. Never found one of those.
Thanks
Roger
Roger,
With black tank open and drained, close third valve, open gray tank that has lots of water in it for a count of two and then close grey tank.
Open third valve and allow the disturbed afluent in the black tank to drain. Repeat till clean.
Close black tank and open grey to allow it to finish draining. No chance of afluent backing up into grey tank with this procedure.
Hope this helps.
That is the procedure I use to empty the tanks.
There is no check valve.
The tanks will equalize to the same level and should not overflow.
You don't need to wait until they equalize to shut the grey valve. It only needs that initial rush.
Look at the photo of my configuration to see it would be difficult to back up into the grey, which really is not an issue if it does.
It is all emptying into the same place.
I have never seen any solids come out of my grey tank.
When you close the black tank valve you are emptying the grey water directly.
I think it does help to open the grey into the black to dislodge any thing still in there as I always see additional solids coming out while doing it after I thought it was clean.
When you back flush the black tank with the grey water, there is a mixing of the two tanks water. Most if not all of the solids should have emptied with black, I have no issues with mix. Even if you choose not to back flush, 3rd valve nice back up to primary valves
I hook up the drain hose and make sure everything is secure and ready, then
open third valve
open black valve, allow full drainage, close third valve
open grey valve, allow full equalization between grey and black tanks, close grey valve
open third valve, allow full drainage, close third valve
repeat a couple of times
after third time dumping black, leave third and black open, the open grey to empty everything
Effluent is usually pretty much soapy grey water after first back flush is drained.
I also put Dawn and some fresh water down the toilet after dumping to provide moisture and surfactant to the black tank. We have overflow traps built into the toilet bowl, and I make sure they are filled with fresh water after I empty the holding tanks.
I have always found it interesting that folks worry about getting black water in to the gray water tank or drain. They are together in a sticks and bricks house and it's no problem. The gray water drains have traps in them that would keep any odor out. Just interesting. ^.^d
Amount of coaches out there including FT Combined black and gray water tank
I totally agree with Larry, to many hours spent on unimportant things like this. I have 3rd valve and do not worrty if grey goes into black (or vice versa) and as Barry said "it all goes the same way anyway"
Do the change Roger and then worry about something important- like is it happy hour yet!
JohnH
Holding tanks are just that - holding tanks. If they are RV waste tanks, it doesn't much matter what is in them as long as they are dumped in the proper dump hole when you dump. Some SOB Class C units dump the shower drain into the black tank. That isn't much fun if you are taking a shower and the tank is almost full and you think it will fit!!!
Thanks, folks.
I am just a really curious sort and want to understand how stuff works. In any case I would prefer to minimize black into gray contamination. I like Rudy's procedure.
My 2001 has 110 gal gray and 54 gal black tank capacity. So if black is empty and gray is getting close to full, equalizing levels shouldn't overfill the black tank.
Thanks for helping me think this through. Another thing on my list (growing) of coach projects. Best to know where I am going and why, at least for me.
Yes, in your home the waste system shares common pipes but you don't have holding tanks in your house. Sinks, showers and any gray water source drain are never in common with black water drains until the main stack. Properly done, black water never goes into the gray water drain lines unles there is a nasty backup. Even when gray water is saved for use in lawn and garden watering it is carefully isolated from black water with an entirely separate plumbing system.
Roger
On my old 93 GV 225 I had a pipe from the bottom of grey tank to top of Black tank and 2 valves and a bilge type pump. If grey was getting full I could send grey water to black tank without touching waste gates. Worked good and at same time helped keep the senders clean on sides.
JohnH
@Roger No need to freak out over black water contaminating the gray water tank. The new IH's only have one tank for gray and black. Seemed strange to me when I first heard it but after thinking about it what difference does it make. It all gets combined at the dump anyway. Boondockers have have been using the 3rd valve to combine tanks for years for extra capacity. The only way you are contaminating anything is if you allow the the tanks fill to the point that they back up into the shower. At that point you have made a huge mistake and need to find a dump right now! Even if that happens it's not a big deal. Dump and then clean the shower with Clorox. Not fun but not a tragedy either. :)
see ya
ken
With our pedal toilet, after we back flushed gray water into black tank, we smelled the gray water when flushing toilet. Seems that gray water smells worse than black water, and washing out the black tank with gray water left the gray smell in the black tank.
On our weekly dumping we feed a city water hose into motorhome and use it to clean toilet & drains, so we don't feel a need to back flush with the 3rd valve anymore.
Been back flushing since my 99 u270 accident in 02. No smells of any king with either the electric toilet or now the new manual one. A full bowl of water goes down after back flushing if hooked to city water.
Lots of opinions on this one. We don't backwash at all. Instead, after dumping the black, We shut the valve and fill the toilet with a couple of gallons of water and give it a flush. That cleans out any remnants and I can see the clear water rushing through. Then close black and dump gray. Finish up with a the Dawn-Calgon treatment along with a bucket of water and we're good to go.
One time I waited behind someone at the dump a looong time. As it happened, it was another Foretravel, a 98. In talking with the dumper he explained to me that when he bought his rig (at Foretravel) they instructed him in the dumping procedure. That procedure entailed the initial black dump followed by two complete backwashes and finally, the gray.
Think I'll stick with the quick and easy.
jor
I solved this problem when I built and installed my own tank flush system. One side benefit is that the system cleans the back side of the tanks where the sensor tape is on the outside,the tank gauges read correctly.
Bill Willet, could you please post a schematic of your plumbing? I'm having some issues with getting accurate readings on my tank levels & I'm currently sitting in a boondock circumstance. Thanks
Fred, you have a different system than the later coaches. There are probes in the tank and the wires are screwed to the probes. On our 84 ored I installed the sea level system as the probes get toilet paper on them and gunk and then do not read right, but the sea level system is not affected that way. If you install the sea level you can use the wires that are already there and remove them from the plug on the panel in your dash. The hardest one is the fresh water tank and being able to place the strips on the tank
As I have posted previously. After draining the black water tank, I just raise the drain hose with the grey water valve open and open the black water valve. Then I close the grey and lower the hose until the black water empties and then replete that a coupe times. I often use dawn down the drains to Help loosen things up. I also tilt the coach to the side to completely drain the tanks.
When I removed my tanks I learned that they are installed on inclined platforms so it's already rolling downhill.
jor
I usually tilt the coach to drain tanks. It seems to me that the system flushes with greater velocity when the coach is tilted. Besides that, I still think it's neat that I can quickly and easily tilt the coach by pressing a couple of buttons. :D
What year did they start adding the Black Tank rinse fitting? I have one on my 2002 U270, but I really don't know when they started doing that. It works great to rinse it out.
WE have black and gray rinse connections on our '96 U295
NOT on our 93 U300.
No tank rinse fittings on our 1997 U295. (They may be well hidden and this could be an operator problem. ;) )
Back wash using grey water works well. Our Polychute waste hose has a couple of sight glasses that allow a view of the effluent. After a couple of back flushes, the effluent from the black tank is grey soapy water.
I bought my coach used so I don't know what was original on it. It did have a black water rinse but on the street side which is only good to wash out the main drain valve. Because I had "stuff" hanging up on the sensors (that are on the curb side) and causing false triggering, I added a second rinse line above the sensor probes on the top of the tank. Both rinse units use a standard RV "city water fill" with a built-in check valve Amazon.com: Valterra A01-0172LFVP 2-3/4" Aluminum Finish Lead-Free Metal Water (http://www.amazon.com/Valterra-A01-0172LFVP-Aluminum-Finish-Lead-Free/dp/B005947Z3M/ref=sr_1_34?ie=UTF8&qid=1397950515&sr=8-34&keywords=RV+water+fill)
The biggest concern with using a rinse line is making sure the flow doesn't reverse and contaminate your fresh water!
There several protections in the system I installed:
1. City Water Fill fitting has a check valve built-in
2. Garden hose "Y" splitter has manual valves.
3. I have a short garden hose attached to the utility bay spigot. I only attach this to the rinse connection when I'm actually doing a rinse and monitoring what is going on. Ideally it would be good to have a back flow preventer on the utility bay spigot; code for most residential outside spigots. I had one on it but it would sometimes release and spray water inside the utility bay - bad for bulkheads. So I opted to take it out and vow to always be present when using the rinse.
To install the rinse that is above the sensors I had to use a hole saw on top of the tank and turn it with a wrench (no space for a drillmotor) - slow going but it's only plastic. I think I also attached a string to the hole saw to make sure I didn't drop it in. I sealed it with 3M 5200 and used stainless screws in the flange of the City Water Fill. Then it was just a matter of cobbling together fittings with a hose that passes back over the top of the tank to where the garden hose "Y" is.
There is another important detail (and I wish I could remember exactly how I did it - it been many years now) but I threaded something to the City Water Fill (on the side that goes inside the tank) to direct the water against the wall with the sensors. It may have been just a 45 degree street elbow but I remember testing the spray pattern before installing it.
It does do the trick. I rarely have false readings and almost always use the sensor flush when dumping.