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Old 04-27-2022, 09:33 AM   #1
levic900rr
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Fresh water pump feed for black tank flush

Hey folks, we do a lot of boondocking and road tripping. Often I end up at a wastewater treatment plant of something dumping tanks on our way home. Most of the time these places dont have rinse water, so I cant use the black tank flush. I end up sitting in the bathroom for 20 mins holding the toilet flush down to "rinse" out the black tank.

It got me thinking. If I add a T, a ball valve and a few check valves from one of my cold water lines into the black tank flush line I could have an "off grid" black tank flush. Utilizing my leftover fresh water to flush the black tank without having the keep the toilet open forever while dumping. I could also take advantage of the sprayer that the black flush uses.

Can anyone see any flaws in this plan before I start cutting?

Thanks
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Old 04-27-2022, 09:38 AM   #2
Terry W.
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On my unit I can take the outside hose and connect it to black tank flush. That's also how I do the antifreeze
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Old 04-27-2022, 09:40 AM   #3
levic900rr
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Originally Posted by Terry W. View Post
On my unit I can take the outside hose and connect it to black tank flush. That's also how I do the antifreeze
My rig doesn't have an outside hose. I did consider building a little piece of house that would let me utilize the outdoor shower and adapt it to a garden hose. That might be a less intrusive solution.
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Old 04-27-2022, 10:16 AM   #4
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Quote:
Originally Posted by levic900rr View Post
Hey folks, we do a lot of boondocking and road tripping. Often I end up at a wastewater treatment plant of something dumping tanks on our way home. Most of the time these places dont have rinse water, so I cant use the black tank flush. I end up sitting in the bathroom for 20 mins holding the toilet flush down to "rinse" out the black tank.

It got me thinking. If I add a T, a ball valve and a few check valves from one of my cold water lines into the black tank flush line I could have an "off grid" black tank flush. Utilizing my leftover fresh water to flush the black tank without having the keep the toilet open forever while dumping. I could also take advantage of the sprayer that the black flush uses.

Can anyone see any flaws in this plan before I start cutting?

Thanks
I would not hard plumb a line from the trailer's drinking water to the black or gray holding tank. That's an invitation to disaster. The odds for a check valve to fail or for any other cross contamination is to great. Do you have an outside shower that you coul;d adapt a garden hose fitting to?
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Old 04-27-2022, 11:05 AM   #5
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Originally Posted by flybouy View Post
I would not hard plumb a line from the trailer's drinking water to the black or gray holding tank. That's an invitation to disaster. The odds for a check valve to fail or for any other cross contamination is to great. Do you have an outside shower that you coul;d adapt a garden hose fitting to?
I'm pretty sure my outside shower (the curly hose that plugs into a hot/cold faucet in the convenience center) gets it's water from the potable water tank. I'm not seeing a real difference between that or a hard plumbed line with a valve. Unless the shower fixture has an air gap incorporated?
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Old 04-27-2022, 11:24 AM   #6
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Originally Posted by levic900rr View Post
Hey folks, we do a lot of boondocking and road tripping. Often I end up at a wastewater treatment plant of something dumping tanks on our way home. Most of the time these places dont have rinse water, so I cant use the black tank flush. I end up sitting in the bathroom for 20 mins holding the toilet flush down to "rinse" out the black tank.

It got me thinking. If I add a T, a ball valve and a few check valves from one of my cold water lines into the black tank flush line I could have an "off grid" black tank flush. Utilizing my leftover fresh water to flush the black tank without having the keep the toilet open forever while dumping. I could also take advantage of the sprayer that the black flush uses.

Can anyone see any flaws in this plan before I start cutting?

Thanks
Other than the aforementioned problem with an air gap between your potable water and waste tank I got to wondering about the duty cycle of the pump you are using to add water to the black tank.
I see you said you operate the pump for 20 minutes at a time, which is a good thing. I checked the specs and the Shurflo Revolution 4008-101-A65 is only rated for intermittent duty. I called to find out what that means and was told it shouldn't be operated for more than 45 minutes per hour with a 15 minute cool down period.
I would file that tidbit as "good to know" information when using the potable water pump to supply water to anything, regardless of the type of delivery system employed.
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Old 04-27-2022, 05:57 PM   #7
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Just a different "take on plumbing"...

I believe the 2020 Passport 239ML has an outside shower ????

If so, rather than "hard plumbing a direct link between the fresh water supply and the black tank flush, why not build a "dedicated black tank flush hose" (something that's typically recommended is to always use a separate hose to flush the black tank) anway... Why not build a dedicated hose to connect between the outside shower and the black tank flush input ??? When needed, just pull the hose out of storage, use it, then roll it back up and store it until next time...
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Old 04-27-2022, 08:07 PM   #8
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I'm pretty sure my outside shower (the curly hose that plugs into a hot/cold faucet in the convenience center) gets it's water from the potable water tank. I'm not seeing a real difference between that or a hard plumbed line with a valve. Unless the shower fixture has an air gap incorporated?
Use a water hose type back flow preventer on the tank flush connection then use the outdoor shower.
I used the outdoor shower on our last 5er, whether using pump or city water, so that I could use a hot water tank flush occasionally.
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Old 04-28-2022, 02:10 AM   #9
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Use a water hose type back flow preventer on the tank flush connection then use the outdoor shower.
I used the outdoor shower on our last 5er, whether using pump or city water, so that I could use a hot water tank flush occasionally.
I was thinking a hot water flush might not be a bad idea.
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Old 04-28-2022, 11:05 AM   #10
levic900rr
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Thanks for all the feedback folks. Great info on the cycle times. I GUESSED 20 mins running the pump but in reality its probably less than that. My thought process was that the pump could handle it because I don't run it longer than a typical army shower and we do that all the time.
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Old 04-28-2022, 11:48 AM   #11
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If you look at the specs on the pump they are typically rated for 3 to 5 gal/min. So depending on tank size your likely going to run out of water before exhausting the run time.
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Old 04-28-2022, 04:33 PM   #12
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OK, I'll jump in and suggest a completely different alternative solution.

I am assuming your black tank and grey tank outlet valves flow to a single outlet. If so, here is a much better solution to flush your black tank .... back flush it.

If both the grey and black tanks flow to a single outlet, then here is how you do it.

First, you purchase a 3rd valve, like a Flush King (click here) and attach it to the sewer outlets on your camper. The reason I suggest something like the Flush King, is because it comes witha clear section of pipe, so you can see the contents as the tanks drain. This is really important.

First, attach the Flush King (or an equivalent valve). Open the flush king and open the black tank and drain the black tank. When it stops running (because you can see it) go to set 2.

Next step, close the Flush King valve. Leave open the black tank valve, and now open the grey tank valve. The black tank is empty, all the water from the grey tank will now flush backwards into the black tank. It takes about 10-15 seconds for the two tanks to equalize with approximately the same amount of (grey) water in both tanks now.

Next, close the grey valve, leave the black tank open, and now, open the Flush King so the black tank will flush completely again. Once the black tank finishes again, repeat this proces. You can do it comfortable 3 times if the grey tank is full. Of course, each time you back flush, you are draining the grey water 1/2. then the second time 1/2 of that. then the third time 1/2 of that.

After flushing your black tank 3 times, then use the remaining grey water, which will be 1/8 of the original amount of water in the grey tank to flush out your sewer hose.

Doing so will eliminate, pretty much, the need to flush additional water down the toilet by holding your foot on the pedal, or using a black tank flusher. This recycles the grey water, save water, and is really much easier than your proposed plan. The secret to this success is to do this EVERY time you dump your black tank. Your black tank will always be cleaned out, as good as flushing or better, and really, takes no extra amount of time than normal dumping. Well, maybe a couple minutes to allow the back flush to fill the black tank.

Anyway, think about this and try it before jumping in and doing some alternative plumbing.

I have found, after doing the back-flush 3 times method, when I DO run the black tank flusher, it's already pretty much cleaned out. So, I almost never use my black tank flusher, even though I do try every now and then.
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Old 05-02-2022, 06:51 PM   #13
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Dutchmensport - I like that, simple and effective.
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Old 05-12-2022, 07:58 AM   #14
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Talking

Quote:
Originally Posted by levic900rr View Post
Hey folks, we do a lot of boondocking and road tripping. Often I end up at a wastewater treatment plant of something dumping tanks on our way home. Most of the time these places dont have rinse water, so I cant use the black tank flush. I end up sitting in the bathroom for 20 mins holding the toilet flush down to "rinse" out the black tank.

It got me thinking. If I add a T, a ball valve and a few check valves from one of my cold water lines into the black tank flush line I could have an "off grid" black tank flush. Utilizing my leftover fresh water to flush the black tank without having the keep the toilet open forever while dumping. I could also take advantage of the sprayer that the black flush uses.

Can anyone see any flaws in this plan before I start cutting?

Thanks
Why are you trying to reinvent the wheel? If you use a microbial tank treatment like “Unique rv digest-it” black tank treatment, you do not need to flush your black tank every time you dump. In fact, the instructions say you should NOT flush your tank. It flushes the microbes along with everything else. I have used this product for a few years now with NO issues. This is perfect for boondockers. The microbes breakdown and literally eat poop and clean your black tank including TP. The only time you want to flush your tank is before you put it in storage for several months. You can get this from Amazon, Walmart, and other places. Google it and read up on what it is and how it works. Save yourself some headaches and an unnecessary project. Camco also makes a similar product. In fact the only time I have truly flushed my black tanks is when I prep for winter. Check it out. Its s great product. Happy camping!!
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Old 05-12-2022, 08:01 AM   #15
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Black tank flush

We do the same thing as Dutchmensport does. A day or so before leaving the site, I close off the grey water valve and let the tank fill up. We've come up with the formula that three showers and it's about full. Of course, the indicator lights tell the story too. We also let the galley tank (if you have one) fill and use it for the "back flush" as well. Between the two of them the black tank gets pretty well flushed out. In our case, the galley tank sits higher than the black tank, so ALL if its contents go into the black. Perhaps midway through the season, and definitely at the end of the season, we'll use the built-in spray wash to clean the black tank thoroughly, as the back wash method doesn't necessarily get everything clear to the top of the black tank. Just a little insurance at the end of the season.
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Old 05-12-2022, 11:40 AM   #16
Life-in-Him
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grey water to black tank back flush

Both of our sons use this method.
They have "hassled" us for not doing it or even trying it more.
Having been long time on the road workers I'm sure they've been successful & not having flush ports on their rigs, it seems to make sense.
I only tried it 1 time & it seemed to work, but I keep forgetting to try it again. Senioritis I guess.
Since today is dumpday @ one sons place, I guess it's time to try it again.


Quote:
Originally Posted by dutchmensport View Post
OK, I'll jump in and suggest a completely different alternative solution.

I am assuming your black tank and grey tank outlet valves flow to a single outlet. If so, here is a much better solution to flush your black tank .... back flush it.

If both the grey and black tanks flow to a single outlet, then here is how you do it.

First, you purchase a 3rd valve, like a Flush King (click here) and attach it to the sewer outlets on your camper. The reason I suggest something like the Flush King, is because it comes witha clear section of pipe, so you can see the contents as the tanks drain. This is really important.

First, attach the Flush King (or an equivalent valve). Open the flush king and open the black tank and drain the black tank. When it stops running (because you can see it) go to set 2.

Next step, close the Flush King valve. Leave open the black tank valve, and now open the grey tank valve. The black tank is empty, all the water from the grey tank will now flush backwards into the black tank. It takes about 10-15 seconds for the two tanks to equalize with approximately the same amount of (grey) water in both tanks now.

Next, close the grey valve, leave the black tank open, and now, open the Flush King so the black tank will flush completely again. Once the black tank finishes again, repeat this proces. You can do it comfortable 3 times if the grey tank is full. Of course, each time you back flush, you are draining the grey water 1/2. then the second time 1/2 of that. then the third time 1/2 of that.

After flushing your black tank 3 times, then use the remaining grey water, which will be 1/8 of the original amount of water in the grey tank to flush out your sewer hose.

Doing so will eliminate, pretty much, the need to flush additional water down the toilet by holding your foot on the pedal, or using a black tank flusher. This recycles the grey water, save water, and is really much easier than your proposed plan. The secret to this success is to do this EVERY time you dump your black tank. Your black tank will always be cleaned out, as good as flushing or better, and really, takes no extra amount of time than normal dumping. Well, maybe a couple minutes to allow the back flush to fill the black tank.

Anyway, think about this and try it before jumping in and doing some alternative plumbing.

I have found, after doing the back-flush 3 times method, when I DO run the black tank flusher, it's already pretty much cleaned out. So, I almost never use my black tank flusher, even though I do try every now and then.
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Old 05-12-2022, 02:03 PM   #17
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takpak- what is a galley tank ?
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Old 05-12-2022, 07:49 PM   #18
Life-in-Him
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alternative black tank flushing

My last post I said I'd tryed the Gray tank back flush method 1 time.
Today being dump day I used that method again.
LSS (Long story Short) it works very well. Sewage in the clear elbow/gate valve was the same as 10-15 min of flush port use. Had enough gray water for 4 cycles.

Long story is we installed a Y before the clear gate (both were 45° making a full 90 to relieve stress on connections). The Y coupling came apart @ the joint.
After shutting off the black tank gate we were ready for a shower & laundry run.
Reassembled everything w/o the Y to finish the dump. & Wash down the area.
Net of it all is we emptied the Black tank.
Closed the clear elbow gate.
Opened both black & gray #1.
Let those tanks balance out
Closed gray#1
Opened 45° clear elbow gate valve.
Let black tank empty.
Closed elbow gate.
Opened gray #1
Let B & G1 balance.
Close G#1
Dump B again.
Close elbow
Open G#1 let B & G#1 balance
Total 4 cycles

On last E-gate closure, the flush out of B was basically clear
Closed both B & G#1 valves..

We used the backfush port of our clear gate assembly to wash out the B & G#1 areas & saw no residue from the Black tank.

For years we've "ALWAYS" opened the Gray Valve 1st to check for leaks. Didn't follow our check list & guess what?

Other than the Black tank shower & cleanup. I've been convinced.
Uses a lot less water & clears the slinky much better.

As to the exploding Y, I plan on finding a better product with stronger connection between the coupler with the ears & the body of the Y.





Quote:
Originally Posted by Life-in-Him View Post
Both of our sons use this method.
They have "hassled" us for not doing it or even trying it more.
Having been long time on the road workers I'm sure they've been successful & not having flush ports on their rigs, it seems to make sense.
I only tried it 1 time & it seemed to work, but I keep forgetting to try it again. Senioritis I guess.
Since today is dumpday @ one sons place, I guess it's time to try it again.
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Old 05-12-2022, 07:52 PM   #19
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galley tank

Our cougar has 3 waste tanks.
Black
Gray #1 for shower & sink
Gray#2 (galley tank) for kitchen

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takpak- what is a galley tank ?
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Old 05-12-2022, 08:12 PM   #20
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Our cougar has 3 waste tanks.
Black
Gray #1 for shower & sink
Gray#2 (galley tank) for kitchen
Thank You !
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