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Old 10-26-2018, 06:32 PM   #1
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2010 30' Classic
Tyler , Texas
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Replacing the Black Tank Back Flush

I have a 2010 30 ft. Classic Limited with a black tank back flush that no longer sprays water. I fear it became blocked on our Alaska trip. I have tried everything that has been suggested from air pressure to CLR and filling the tank with water and chlorox. Nothing has worked. I will have to drop the tank cover under the trailer to access the flush valve. Question is, how difficult is it and are the tanks actually being held up by the cover? All suggestions welcome.
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Old 10-26-2018, 06:42 PM   #2
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Don't give up on it yet. I had a similar problem and bought the back flush thing, filled the tank about five times and back flushed about ten times while keeping some water pressure on the black tank flush. It finally opened or whatever and works great now. Try everything possible before you drop the tank. I believe you can get it dislodged with continual effort. Good luck.
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Old 10-26-2018, 07:05 PM   #3
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Actually there is another option. You can cut an access door in the tank cover that will give you access to the tank flush nozzle. The bonus to doing this, the same opening will give access to the dump valves for both valves and possibly to the tank level sensors.
You can see what I did here>
http://www.airforums.com/forums/f444...es-162941.html
Though I did not replace the backflush nozzle, it is just above the valves I replaced.
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Old 10-26-2018, 07:24 PM   #4
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Another couple of thoughts:
A friend of mine has a trailer that had exactly the same issue you are describing. His back flow preventer/anti-siphon valve was stuck and would not let water pass through the black tank flush. Replaced it, problem solved. I think the valve in your trailer is above the water heater inside the bath cabinet.

On my trailer's black tank the flush valve nozzle is within 1/2" of the top of the tank. If you did not have the tank 100% full it would not have been soaking in the solution you put in the tank.
If you try to soak again, try using a mixture of liquid dishwashing detergent and Calgon water softener instead of bleach, the Geo Method type of mix. (https://sites.google.com/site/cbruni/)
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Old 10-27-2018, 09:41 AM   #5
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My 2015 FC20 came with a brass vacuum breaker valve and a plastic check valve on the BW flushing line, which on my trailer is hidden under the bathroom counter. The guts inside the plastic check valve broke, which totally prevented any water from getting to the flushing nozzle. I replaced the check valve with a Shark Bite check valve from Ace Hardware and it now works great! You might want to check yours before you start going after the BW tank and pan.
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Old 10-27-2018, 10:27 AM   #6
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Black Tank Flush / Valves / Sewer Smell



2018 25FB International Serenity

My anti-siphon vacuum break and check valve are in the back of the closet in between the refrigerator and shower. removed small panel to access. see image attached here.

I had the same issue, black tank flush spray was blocked. I am pretty sure it was because we didn't have a pressure regulator on the flush hose and it forced either the vacuum break and check valve to get stuck. I thought I fixed it by unhooking one end of the check valve and then turning the hose on for just a second running water through it, which unblocked the flow. However, over the next month, a terrible smell permeated the closet. Once I unclogged the issue, I think it was broken (vacuum break is my guess) and the sewer gas leaked back and out the top.

here is what I went through to fix.

1) Cleaned black tank with detergents, etc. as everyone suggested. Didn't fix the issue.

2) Climbed on top of the airstream and took off the black water tank vent and ran house through the vent to see if something was stuck inside. Water ran out into sewer no problem. This wasn't the issue.

3) I figured then it had to be the vacuum break or plastic check valve I thought I fixed months earlier.

4) So, easy, just replace the valves, right? Not so easy as you can't go to Home Depot or even an RV store like Camping World and just pick up the valves to replace. The smell was so bad that I had to go to Home Depot and just get fittings to replace the broken pieces temporarily (no vacuum break, jsut brass fittings) while I ordered the valves online. When I removed the original valves and replace with temp fitting the smell stopped.

I am waiting for the valves to come from Amazon and I will replace temp fitting with new vacuum and check valves. I hope this will get it for me.

Valves at Amazon

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

https://www.amazon.com/Zurn-Q2500-Mp...GSVW766DA83RDR
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Old 10-27-2018, 11:36 AM   #7
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Quote:
Originally Posted by patrick p View Post
I have a 2010 30 ft. Classic Limited with a black tank back flush that no longer sprays water. I fear it became blocked on our Alaska trip. I have tried everything that has been suggested from air pressure to CLR and filling the tank with water and chlorox. Nothing has worked. I will have to drop the tank cover under the trailer to access the flush valve. Question is, how difficult is it and are the tanks actually being held up by the cover? All suggestions welcome.
I would try all the above before dropping the black tank.
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Old 10-27-2018, 12:55 PM   #8
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I was following this Thread on my I-phone and saw a post from a gentleman who included 2 links to Amazon for the check valve and anti-siphon valve (?). I am now at my desk top computer so I could print the links. I am on the tread but cannot find the gentleman's post. (On either my I-phone or desk-top computer) Why???? Any help would be appreciated.
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Old 10-27-2018, 01:04 PM   #9
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I bought a 2018 25ft FB and the the first trip mine quite working. I thing if you use a hose that has and dirt or sand in it or you drag it on the ground and you don’t know there is sand in the end of the hose it can clog up the check valve in the line going to the black tank. You will have to change the check valve. I also suggest purchasing a washer to place where you attach the hose on the trailer that has a fine screen to keep dirt or rubber from the hose from getting into the system. Some campgrounds May use well water and could be dirty.
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Old 10-27-2018, 01:11 PM   #10
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Check valve
http://odmrv.com/catalog/index.php?m...roducts_id=901

Check valve
https://www.amazon.com/Valterra-P234...rv+check+valve

Anti-siphon valve installed by Airstream (I would not replace it with the same type).
http://odmrv.com/catalog/index.php?m...oducts_id=1601

Anti-siphon, the type that will not break under normal/high water pressure
https://www.amazon.com/Cash-Acme-173...i+siphon+valve
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Old 10-27-2018, 01:46 PM   #11
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Flush King

Buy a flush King at AMAZON or Camping World. Make sure you get the one with two valves or it will not work (not the one at Walmart with one valve). Cost around $35.. Hook the flush King up to your sewer tank outlet. Back fill your tank a little at a time. Open the flush King valve. After a few times it will unclog your sewer and drain the tank. Did it for a neighbor last year who’s 5th wheel with the sewage drain completely blocked. After a few back fills it was draining perfectly.
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Old 10-27-2018, 02:19 PM   #12
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Quote:
Originally Posted by A W Warn View Post
Another couple of thoughts:
A friend of mine has a trailer that had exactly the same issue you are describing. His back flow preventer/anti-siphon valve was stuck and would not let water pass through the black tank flush. Replaced it, problem solved. I think the valve in your trailer is above the water heater inside the bath cabinet.
This is likely. Replace the anti-siphon valve that can be found inside the trailer, somewhere near where the flush is on the outside.
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Old 10-27-2018, 07:12 PM   #13
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Thank you all for your responses. I did cut an inspection hole in the bottom of the pan but wasn't large enough. I will cut a larger hole which should give me access. I have replaced the anti-siphon valve and the check valve but replaced it with another plastic one. I have ordered the brass anti-siphon valve as well as the brass check valve. I will surely try the water softener and bleach. Again, thanks for the help.
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Old 10-27-2018, 09:06 PM   #14
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Quote:
Originally Posted by A W Warn View Post
Actually there is another option. You can cut an access door in the tank cover that will give you access to the tank flush nozzle. The bonus to doing this, the same opening will give access to the dump valves for both valves and possibly to the tank level sensors.
You can see what I did here>
http://www.airforums.com/forums/f444...es-162941.html
Though I did not replace the backflush nozzle, it is just above the valves I replaced.
Alan,

Can you give a pointer or two on how to cut a hole in the pan? What tool to use? And how not to puncture the tank in the process?
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Old 10-28-2018, 06:41 AM   #15
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Alan,

Can you give a pointer or two on how to cut a hole in the pan? What tool to use? And how not to puncture the tank in the process?
Post #4, above in this thread has a link to a thread with photos.

I started by using a framing square, marking the area I wanted to remove. Then cut a small hole in the metal to insert the tips of aviation snips.(a Dremel tool or grinder would work if the depth of cut could be controlled. Wires, pipes, tanks)
I have arthritis in my hands and it was difficult for me to continue with the snips so I purchased a electric nibbler to complete the cutting. I used a file to dull sharp edges. After completing the work I made a cover out of scrap metal that is held in place by sheet metal screws.

I used a flashlight to look inside the tank in the slots where the handles protrude. There are wires for the sensors laying loose, so you have to be careful with the cutting device. Between the valves where there is no tank is the location I cut first. I started small near the center creating a hand sized hole, working toward the perimeter. The cutout I made was 20" front to back, 18" side to side.

Leave the bent metal corners of the tank intact. This keeps the original rigidity/strength of the pan.
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Old 10-28-2018, 07:15 AM   #16
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edit to above:
Leave the bent metal corners of the tank pan intact. This keeps the original rigidity/strength of the pan.

Another thing to note:
If there has been no prior change, there should be insulation between the pan and tank that allows ~1/2" space for cutting.
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Old 10-28-2018, 07:35 AM   #17
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Wetfeet....any chance you can post a picture of where the valve is under the sink? Also, maybe post it in the FC20 section of this forum as well.
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Old 10-28-2018, 05:20 PM   #18
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Patrick, Hope you got the black tank washer working again. I had a similar problem that had a simpler solution; keep in mind this was with an AS motorhome vs trailer so everything is bigger...haha

After taking half of the sprayer apart from the outside, decided to try cleaning the inside. For those without tank sprayers, Camping World sells a flex hose attachment that is put into the toilet and used to spray the black tank. It has a much stronger sprayer that can be directed all over. Apparently mine did have some sand in it (from un-named FL Campground with ground water) which clogged up my sink faucets too. After a heavy spray down and fill/drain of the black tank 3 times.....its working again. Fortunately did not have to drop the black tank or drill into it.

Will post more about FL groundwater problems in a different forum. Do not want to highjack this one on black tank maintenance.
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Old 10-29-2018, 08:46 AM   #19
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Sorry, to take a picture of the BW vacuum breaker and check valve requires first removing the toilet and then removing the sheet metal cover behind it that hides some plumbing. I’m on a trip now and I already had to remove the toilet once to fix a leaking flush valve, and i’m not going to do that again. Trust me, once the toilet and the metal cover are gone it’s easy to see.
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Old 10-29-2018, 11:15 PM   #20
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Alan, thanks for the details, and the descriptions and pictures in the other thread. I understand much better now.
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