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Old 04-13-2021, 05:43 AM   #1
colouiss651
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Unhappy Black Tank Flush blockage

Hi there Gang from Colorado. Does anyone out there have any knowledge of how to clear a blockage at the black tank flush? The symptom is that fresh water is spaying out of a pressure relief valve which is located in the bathroom base cabinet. The flush line comes from the water service port into the cabinet on its way to the flush tank. Under the sink the line is intersected by this plastic valve then goes on to the tank. The water is not making it to the tank (no, it is not frozen). The black tank release valve is open and the tank is empty. The camper is a 2018 Outback 298RE if that helps. The last time it was used was last fall. When I tried to flush it for the first time this spring is when it backed up water into the camper. All other plumbing is working fine and was winterized (of course there is no way to winterize this line-it doesnt appear to be a rupture anyway). Tech support is scratching their heads and want to send out a mobile tech to drop the belly line etc.
18 years of owning campers and this is a first.
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Old 04-13-2021, 05:52 AM   #2
flybouy
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That is not a pressure relief valve it is a vacume break or antisiphone valve. I don't know what "tech support" you're talking about but that's a very common device that fails with regularity. You can remove and replace it for a few dollars. The toughest part is getting to it as it's often up high behind the bathroom sink.
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Old 04-13-2021, 05:58 AM   #3
chuckster57
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I would remove the anti siphon valve, and use low pressure air (10-20 PSI) and see if you can clear it. I have had to drop the underbelly and pull the rinser out of the tank before. The nozzle holes are very small and I had to use a pick.
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Old 04-13-2021, 06:07 AM   #4
Javi
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Originally Posted by colouiss651 View Post
Hi there Gang from Colorado. Does anyone out there have any knowledge of how to clear a blockage at the black tank flush? The symptom is that fresh water is spaying out of a pressure relief valve which is located in the bathroom base cabinet. The flush line comes from the water service port into the cabinet on its way to the flush tank. Under the sink the line is intersected by this plastic valve then goes on to the tank. The water is not making it to the tank (no, it is not frozen). The black tank release valve is open and the tank is empty. The camper is a 2018 Outback 298RE if that helps. The last time it was used was last fall. When I tried to flush it for the first time this spring is when it backed up water into the camper. All other plumbing is working fine and was winterized (of course there is no way to winterize this line-it doesnt appear to be a rupture anyway). Tech support is scratching their heads and want to send out a mobile tech to drop the belly line etc.
18 years of owning campers and this is a first.


Quote:
Originally Posted by flybouy View Post
That is not a pressure relief valve it is a vacume break or antisiphone valve. I don't know what "tech support" you're talking about but that's a very common device that fails with regularity. You can remove and replace it for a few dollars. The toughest part is getting to it as it's often up high behind the bathroom sink.
Almost the first thing I do to a new trailer when I pick it up is replace the anti-siphon valve with 2 90` fittings and a bit of PEX.. then I use a hose bib anti-siphon fitting and pressure regulator at the hydrant.

Funny thing is... I've never had a leak

OH YEAH... the spray bar is probably not blocked... just the valve leaking..
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Old 04-13-2021, 06:54 AM   #5
colouiss651
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Quote:
Originally Posted by flybouy View Post
That is not a pressure relief valve it is a vacume break or antisiphone valve. I don't know what "tech support" you're talking about but that's a very common device that fails with regularity. You can remove and replace it for a few dollars. The toughest part is getting to it as it's often up high behind the bathroom sink.
Thanks much. I will try replacing that. In troubleshooting this, I tried forcing 150psi air into the tank after disconnecting the valve. It made no sense to me that air would not go into the tank. Does that make a difference?
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Old 04-13-2021, 07:12 AM   #6
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Be very careful when using air pressure. The pipe n fittings are not made for high pressure. Normally about 30-40 psi is all u want to try
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Old 04-13-2021, 07:13 AM   #7
Javi
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Originally Posted by colouiss651 View Post
Thanks much. I will try replacing that. In troubleshooting this, I tried forcing 150psi air into the tank after disconnecting the valve. It made no sense to me that air would not go into the tank. Does that make a difference?
The holes are very small and any real volume of air would backflow especially at 150 psi.. The spray bar is only designed for 40-50 PSI.. If you didn't blow it apart... I'd just make up two 90 degree PEX fittings with 2" of 1/2" PEX between them to replace the fitting and then hook a regulated water hose to it and see if water runs through it..
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Old 04-13-2021, 09:13 AM   #8
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Originally Posted by Javi View Post
(snip) then I use a hose bib anti-siphon fitting and pressure regulator at the hydrant.
Educate me. What is a “hydrant?”
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Old 04-13-2021, 09:28 AM   #9
JRTJH
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Originally Posted by skids View Post
Educate me. What is a “hydrant?”
https://www.zoro.com/woodford-mfg-fr...-3/i/G1141743/

The "typical" fresh water connection used in all COE and many State and public campgrounds in areas where the temperature falls low enough to cause freeze damage to a conventional "spigot".
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Old 04-13-2021, 10:01 AM   #10
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Thanks John. I wondered what those were called.
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Old 04-13-2021, 10:25 AM   #11
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If don't have one of these get one ASAP & use it at whatever hydrant or spigot you connect your rv water hose to, it will keep your water pressure regulated.

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If you have one of these, save as a spare or toss it, it restricts the flow regardless of pressure.
Click image for larger version

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Also if you don't have an EMS/surge protector (EMS is required) connected to the incoming powers source, get one of them also ASAP & use every time you connect your shore power. The EMS will protect your sensitive electronic equipment from most every type of electrical fault.
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