Sundance - Master Black Tank Flush

I went to flush the master black water in my Sundance 3700RB yesterday and it wouldn't run. The line was pressurized but no water. Is there a valve hidden behind a compartment somewhere that I wasn't aware of to open it up? The rear bathroom worked and no issues.
 
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Re: ATF: Sundance - Master Black Tank Flush

We’ve been out 7 times this year but first time using flush.


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danemayer

Well-known member
Re: ATF: Sundance - Master Black Tank Flush

There are 2 main possibilities.

The black tank flush line has an Anti Siphon Valve between where you attach the hose and where the line connects to the black tank. Once in a while the PEX lines connecting to the Valve are reversed and because the Valve is doing its job, water won't flow. Many trailers have a 6" access port in the shower, behind which you'll usually find the Anti Siphon Valve. Sometimes there are other access routes, so you may have to do a little hunting.

It's also possible one of the PEX lines has been pinched or otherwise restricted. You may have to hunt to trace the PEX lines.
 

Gary521

Well-known member
A lot of us have bypassed the valve altogether. Mine did not work from new. In addition, part of the water lines to the black tank are flexible. Check for a kink.
 
I'm just trying to find it first. I checked the access in the shower and didn't find anything but I didn't think to feel above the valve. I have read some people say it is by the toilet. Once I find it I will bypass it. What is your recommendation on how do do that? Sharkbite the fittings together?
 
does anyone have a picture of their bypass set up? I did see another thread as this issue seems to be known and popular issue. Thank you
 

danemayer

Well-known member
The attached picture is from the backside of the bathroom on a Bighorn. Taken at the factory before the exterior wall was mounted.
 

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Mine appears to be under the sink. Now to confirm it is on correctly and if not then look for a kink somewhere. Thanks for the feedback


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Yep it was reversed. Now in order to have the air gap portion on top and level I need to change the fittings around.


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JohnDar

Prolifically Gabby Member
When mine failed and dumped water onto the floor inside by the steps and door, I had to pull the lines down from the wall cavity behind the toilet. I replaced it with a Sharkbite check valve. In my opinion, anti-siphon valves, sill cocks, and the idea in general is a joke. I have a large one in our home lawn sprinkler and it leaks. The two outdoor sill cocks are anti-siphon and they leak when I use them. Have from day one.

When was the last time your water system went into negative pressure and sucked water back into it?


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Gary521

Well-known member
On the backside of the UDC follow the water line from the tank flush connection. You will see it heading up toward the wall. You will also see another line next to it heading down and connecting to a flexible line. Those are the flush lines. You could cut the PEX lines and spice them together with sharkbite. I removed the line from the back of the UDC connector. I replaced the UDC connector with one that has a check valve built in. From the new connector, I ran a new flexible line to the flexible line going to the black tank. Flexible line and hose fittings from Ace Hardware. New connector from any RV supply. You could splice in a check valve and not replace the connector. Just the way I did it. Check valve prevents any possibility of back flow out the connector into the hose.
 

cookie

Administrator
Staff member
The only way the warranty would be voided is if the mod you make causes a problem.

Peace
Dave
 
And, you can add a 2019 Sundance 283RB to the list. Two black water tanks and neither will flush. My poor service department was no help — the tech thought it might be kinked lines but they don’t have a dump station to test the system. I shall now search for the infamous check valves and fix’em on me own!

Doc
 

AndrewAbb

Member
HI All,

I have a 2018 Sundance 283 Rb.

I am trying to determine the right method of flushing my black tanks. I am under the impression it has two. Once for the Master bath and one for the Rear Bunk 1/2 Bath.

IS the flush system routed to both black tanks?

If I use the recommended 5 minute flush will this fill up both tanks? and can i separately dump the black tanks after or will I have to have them connected to eachother.

This is all dependent on if the flush system works which doesn't look super promising given the thread.

Thanks alot,

Andrew
 

JohnDar

Prolifically Gabby Member
HI All,

I have a 2018 Sundance 283 Rb.

I am trying to determine the right method of flushing my black tanks. I am under the impression it has two. Once for the Master bath and one for the Rear Bunk 1/2 Bath.

IS the flush system routed to both black tanks?

If I use the recommended 5 minute flush will this fill up both tanks? and can i separately dump the black tanks after or will I have to have them connected to eachother.

This is all dependent on if the flush system works which doesn't look super promising given the thread.

Thanks alot,

Andrew

Get yourself a battery powered water flow meter(they’re cheap) that attaches to the hose to track how many gallons you’re putting in relative to the tank capacity. With that you’ll never overfill the black tanks or even your fresh water one.


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AndrewAbb

Member
Hi thanks for the response.

I am still trying to determine the size of the 2nd black water tank for the rear bunk 1/2 bath

If anyone has this information that would be great.

Thanks
 
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