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Old 08-24-2019, 07:01 AM   #1
Bamabox
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Using fresh tank and water pump for black tank flush?

This winds up being an issue at dump stations. When at full hookups, total non-issue as you have water and sewer is connected. My 2017 21RBS has a black tank flush line in the exterior water control center. And it works amazingly well. Don’t know what the spray pattern is inside the tank, but if I run it long enough with the black tank valve open and watching through the clear plastic extension on the dump pipe, it appears to get out everything and will run very clear. But at most of the dump stations I’ve been to , there’s no place to hook up a hose. Water for rinsing the area, but no hose bib. And of course there’s the issue of being a slow poke at the dump station when checkout is 11 am and there’s a line behind you 3-4 deep. So I’m wondering if anybody has done a mod where they can use the water pump and fresh tank water to run that BT flush while at the dump station? First thought was a T valve for the pump to either send water to all the normal lines, or send it to the BT flush line. That would be a pita however, as my pump and lines are up front by the bed and front is blocked off by the slide. I do have a exterior hot/cold faucet quick disconnect style right in the water command center where I might be able to fabricate a small section of hose to go from the faucet to the BT female connection. They are literally 4” apart. That quick disconnect looks pretty restrictive size wise, and wondering if it would give enough volume for an efficient flush. Would not be concerned about pump volume, as I seem to get more water volume and pressure from the pump than I do when using the “city water” connection with one of those cheap brass restrictors.
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Old 08-24-2019, 07:36 AM   #2
JRTJH
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Black tank flushing is more "time dependent" than "volume dependent" given the limited water being sprayed into the black tank by either the campground supply or by any "on-board supply" of water.

That said, and by what you stated, "...but if I run it long enough with the black tank valve open and watching through the clear plastic extension on the dump pipe, it appears to get out everything and will run very clear." Usually, there's simply not enough time at a busy dump site to take the necessary time to flush "until it runs very clear". If you did, you'd either find someone behind you honking their horn or confronting you to get out of the damn way..... (this isn't a lesson in dump station etiquette but just a statement that people behind you may well take offense to your plan)....

An alternative that works for me, takes 10-15 seconds and does a relatively decent job of "initial flush of the big stuff" is this:

Install a terminal valve on the end of your sewer connection and then at the dump station, install the hose on that valve. This will allow you to close off the hose and redirect water "inside the trailer sewer system"...

When at the dump station, dump the black tank and leave the black valve open, then close the terminal valve, open the gray tank valve (this will force large amounts of gray water into the black tank). Listen carefully, you can hear the water flowing from the gray tank into the black tank. Once the sound diminishes a bit (4 or 5 seconds) close the gray tank valve and open the terminal valve. The "gray water rinse" will flow out of the black tank. Once that's drained, you can repeat with the "other gray tank" if your trailer is equipped with two gray tanks, and finally, after the black tank is rinsed (once or twice depending on the trailer configuration), close the black tank valve and open the gray tank valve to flush the sewer hose.

Total added time, about 15-20 seconds, once you figure out the sequence and do it a couple of times.

All of the above must consider this: FIRST and FOREMOST: Black tanks don't have to be cleaned completely at every dump. Second: The busy dump station at a busy campground is NOT the place to do black tank maintenance. Most "conscientious campers" will either schedule their last trip of the season and most "intermittent trips" to include full hookups so they can do their "black tank maintenance" at a private site, not in line on Sunday morning at 11:30 with a line behind them.... Yeah, I know, but we've all seen that "inconsiderate jerk" that cares only about getting every "chunk" out of his black tank while the line behind him is backed up all the way to the turnoff to the dump station..... Don't be one of those people, plan your full hookup sites so you can "regularly flush your black tank" while not being the jerk......
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Old 08-24-2019, 11:36 AM   #3
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I have a 22RBS and I could hook up the outside shower hose to the flush connection very easy. But like you I'm not sure if it would give me the flow rate needed to get a good flush. If you want to get fancy just drop the underbelly back by the dump valves and you could tap into the flushing line and the water lines and bring them out to the side of the trailer where you could connect a hose to tie them together when you want to.

I actually considered doing something like that but only tee in the flush line so I could hook up a flush hose right at the dump valve area instead of fooling around with the convenience center connection.

And I agree with John I'm not worried about flushing the tank every time. Also I'm lucky enough to live in a rural area and can flush the tank as much as I want to at home!
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Old 08-24-2019, 01:29 PM   #4
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Agree with John!
It's not so much the spray of the tank flush as much as the volume when you open the valve. You could actually just turn on your pump, or hooked to a faucet, & fill the tank by stepping on the toilet pedal, no plumbing required & you could so do before pulling out of your site & stalling the dump station line.
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Old 08-24-2019, 05:29 PM   #5
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Quote:
Originally Posted by JRTJH View Post
Black tank flushing is more "time dependent" than "volume dependent" given the limited water being sprayed into the black tank by either the campground supply or by any "on-board supply" of water.

That said, and by what you stated, "...but if I run it long enough with the black tank valve open and watching through the clear plastic extension on the dump pipe, it appears to get out everything and will run very clear." Usually, there's simply not enough time at a busy dump site to take the necessary time to flush "until it runs very clear". If you did, you'd either find someone behind you honking their horn or confronting you to get out of the damn way..... (this isn't a lesson in dump station etiquette but just a statement that people behind you may well take offense to your plan)....

An alternative that works for me, takes 10-15 seconds and does a relatively decent job of "initial flush of the big stuff" is this:

Install a terminal valve on the end of your sewer connection and then at the dump station, install the hose on that valve. This will allow you to close off the hose and redirect water "inside the trailer sewer system"...

When at the dump station, dump the black tank and leave the black valve open, then close the terminal valve, open the gray tank valve (this will force large amounts of gray water into the black tank). Listen carefully, you can hear the water flowing from the gray tank into the black tank. Once the sound diminishes a bit (4 or 5 seconds) close the gray tank valve and open the terminal valve. The "gray water rinse" will flow out of the black tank. Once that's drained, you can repeat with the "other gray tank" if your trailer is equipped with two gray tanks, and finally, after the black tank is rinsed (once or twice depending on the trailer configuration), close the black tank valve and open the gray tank valve to flush the sewer hose.

Total added time, about 15-20 seconds, once you figure out the sequence and do it a couple of times.

All of the above must consider this: FIRST and FOREMOST: Black tanks don't have to be cleaned completely at every dump. Second: The busy dump station at a busy campground is NOT the place to do black tank maintenance. Most "conscientious campers" will either schedule their last trip of the season and most "intermittent trips" to include full hookups so they can do their "black tank maintenance" at a private site, not in line on Sunday morning at 11:30 with a line behind them.... Yeah, I know, but we've all seen that "inconsiderate jerk" that cares only about getting every "chunk" out of his black tank while the line behind him is backed up all the way to the turnoff to the dump station..... Don't be one of those people, plan your full hookup sites so you can "regularly flush your black tank" while not being the jerk......
And of course there’s the issue of being a slow poke at the dump station when checkout is 11 am and there’s a line behind you 3-4 deep

I think that issue was acknowledged.
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Old 08-24-2019, 08:50 PM   #6
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I use my outside shower connection to the black tank cleanout sprayer every single time I dump. Works perfect ! If at a dump station and not at a rv site with hookups I will have the outside shower hose pre hooked to the flush to save time.
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Old 08-25-2019, 04:17 AM   #7
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Quote:
Originally Posted by nellie1289 View Post
I use my outside shower connection to the black tank cleanout sprayer every single time I dump. Works perfect ! If at a dump station and not at a rv site with hookups I will have the outside shower hose pre hooked to the flush to save time.
Winner. All pre hooked, hook up sewer hose, open valve, DW turns on the outside shower, no extra time required but a much better clean out. Unhook sewer hose, pull forward out of dump station and unhook shower connection, go inside turn off pump out of everyone’s way. Perfect.
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Old 08-25-2019, 07:54 AM   #8
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No one's worried about stuff slipping back into the freshwater tank? Isn't that the same reason most of us use a different hose for the black tank flush?
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Old 08-25-2019, 08:28 AM   #9
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Quote:
Originally Posted by KSH View Post
No one's worried about stuff slipping back into the freshwater tank? Isn't that the same reason most of us use a different hose for the black tank flush?
Between "defeating/bypassing" the anti-siphon valve, modifying the black tank PEX by adding multiple sources for leaks and using a "direct connection from the black tank to the fresh water system, pump and fresh water tank, I just stopped responding. You're correct in being concerned with "fecal matter contamination" with this kind of "limited protection modification" of the black tank.

But then, I'm not going to be drinking water from that trailer's fresh water source, which is why I stopped responding.......
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Old 08-25-2019, 08:36 AM   #10
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I’d be far more worried about the fresh water connection you are hooking up to at every camp site personally
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Old 08-25-2019, 09:56 AM   #11
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Quote:
Originally Posted by nellie1289 View Post
I’d be far more worried about the fresh water connection you are hooking up to at every camp site personally
Which is why I carried a spray bottle with diluted bleach mixture to spray the faucet before connecting & after disconnecting. Plus had a sediment filter connected to a water softener going into a filter with a charcoal cartridge, drank water from our sink faucet everywhere we parked.
I agree, no direct connection between fresh water & black tank. Some parks the water tasted like $h##, but not after going through my system & there wasn't any connections from my system to get it there.
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Old 09-01-2019, 08:01 AM   #12
OwenMaeGabe
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I carry a 5 gal bucket. When in a dump station I fill it up and pour it into the toilet while draining. Do it when tank is just about empty. I do this several times, depending on the number of rv'ers behind me. Also, the fresh water pressure in a dump site is quite high so I don't hook up to my blank tank flush connection, it will fill up a bucket quick though.
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Old 09-01-2019, 09:04 AM   #13
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Put a cheap pressure regulator on the flushing hose.
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Old 09-02-2019, 02:07 PM   #14
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There is a chock that can be inserted in the bottom of the toilet bowl to hold the flush valve open.
Depress the flush valve, insert plastic chock, flush valve stays open, fresh water pump will pump water into the toilet and BW tank as long as there's water in your fresh tank.
Easy, no mods required.
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Old 09-08-2019, 06:14 AM   #15
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Originally Posted by Bamabox View Post
Winner. All pre hooked, hook up sewer hose, open valve, DW turns on the outside shower, no extra time required but a much better clean out. Unhook sewer hose, pull forward out of dump station and unhook shower connection, go inside turn off pump out of everyone’s way. Perfect.

I also use the outside shower to hook to my black tank flush. I connect it so I am ready to go if I am waiting in line at the dump station. Pump is on and ready, I also make sure my hot water tank is hot and ready to go - I use hot water to do the flush. I am pretty confident I read in my manual there is a check valve on the black tank flush system. I turn on the hot of the outside shower (connected to the tank flush) as I see the black tank is nearing its end through the clear extension I also use.
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