Black tank flush anti siphon valve

Welshdog · 03-13-2022, 07:16 AM

Hi folks!
We have a 2019 Keystone Sprinter 312 MLS Limited travel trailer. Does anyone know where the anti siphon valve for the black tank flush is located? It is not under the bathroom sink, a common location on many rv’s. I would like to know for future potential maintenance. Thanks for any responses/ info.

**JRTJH** · 03-13-2022, 07:23 AM

There are several other places for the anti-siphon valve to be installed, but since about 2017, I've only seen them under the bathroom sink.

Take a look under your sink and count the PEX lines coming up into the vanity. If there are 4 PEX lines, the anti-siphon valve is located there. On my trailer, unless you "literally crawl inside the vanity, turn "belly up" with a flash light, you'll NEVER see the anti-siphon valve".... It's located behind the faucet stem, above the cone washer fitting that connects the hot water PEX to the faucet. It's literally, between the wall and the faucet stem and impossible to see with the sink bowl blocking the view. Even on my back, inside the vanity, I can't see it until I point a flashlight on the hot water stem....

Count the PEX lines, if there's four lines, keep looking under the vanity.

**chuckster57** · 03-13-2022, 07:24 AM

I have seen them in the wall behind the shower faucet.

Welshdog · 03-13-2022, 07:56 AM

Thank you Sir! Will check this out.

Welshdog · 03-13-2022, 09:40 AM

Checked under the vanity and there are just two lines. Red and blue. I know that this back flow line is a white line. Maybe, as suggested by another member it could be in the wall behind the shower faucets. It seems so stupid that this valve is not readily accessible! Thank you again for your response, at least I now know where not to look. Onward and upward!��

**sourdough** · 03-13-2022, 09:58 AM

Your's isn't under the sink as mine is but I do have the red and blue lines for the sink then the white line, both in and out, for the anti siphon valve so figure yours will be the same. Since it's not under the sink hopefully it's behind the shower faucet. Our friends have a Big Horn and they (mobile tech) literally had to cut a hole in the wall of the pass thru under the bathroom to repair his (front bath). Let's hope they didn't do something like that on yours.

**chuckster57** · 03-13-2022, 10:05 AM

If its in the wall behind the shower faucet, then you should be able to take the faucet off and see the lines. Grand Designs did this for years as I remember.

Welshdog · 03-13-2022, 10:07 AM

I’m hoping that this valve is behind the shower faucets and is accessible! Everything is working alright so far, but if it should need attention I want to know where it is. Any problems that are water related need to be dealt with ASAP. Thank you for your response.

**JRTJH** · 03-13-2022, 10:14 AM

Locate the shower faucet, then "imagine where that spot is on the wall in the main cabin"... Go to the main cabin and see if there's a cupboard or cabinet in that space. If so, open the cabinet and see if there's a "cover" screwed to the wall on the rear wall of the cabinet. If so, remove that cover, you may find the anti-siphon valve there.

If there's no cabinet on that wall in the main cabin, then go back to the shower, carefully remove the faucet and backer panel from the wall. There should be enough length in the PEX lines to pull the faucet to one side. Use a flashlight and a mirror to see if you can find the anti-siphon valve between the shower wall and the main cabin wall....

It'll look something like these photos

Welshdog · 03-13-2022, 10:17 AM

Thank you Chuckster, hopefully this is the case! I had a bad leak yesterday where the black tank flush port is set in the rv wall. Took the port out and saw it was a worn cone washer, and, the water line fitting was slightly loose too. Easy fix luckily! That got me thinking about the check valve……! I’ve had to tighten several water line fittings on this rv, all were minor leaks thankfully. Prevention is way better than cure every time.
Thanks again!

Welshdog · 03-13-2022, 10:22 AM

Thank you that’s great information. I have a strong feeling it’s in the wall behind the shower faucets. Hopefully there’s enough slack to gain access if needed. I don’t like the idea of this valve being a cheap plastic one, I would like to replace it with a more substantial unit.

**sourdough** · 03-13-2022, 10:32 AM

Some folks have replaced them with more robust valves and others like myself have just cut them out, placed 90s on the water lines and eliminated the whole thing. I do have hose end anti siphon valve on the inlet for the black tank flush outside in the event some kind of failure might happen. I strongly doubt that given the circumstances that would be required to siphon water back into the water supply and the fact I'm standing there the entire time.

Gary R. · 03-13-2022, 10:32 AM

The black tank flush has never worked in our Alpine, so one day I went on a quest to find the valve.

Wasn't under the lavatory sink, as only two Pex lines are visible.

So, with advice from the folks here, I carefully removed the shower faucet, and had just a second to see the valve before it fell down to the floor behind the shower.

Given the very small access area, I decided to forget about it and reinstalled the faucet.

I would like to have a conversation with the person at the factory who decided to put it there....

Cheers!

Welshdog · 03-13-2022, 10:39 AM

That actually sounds like a good idea to me! I will definitely consider this. Thank you.

Welshdog · 03-13-2022, 10:40 AM

Jeez! That really sucks. Sorry!

**sourdough** · 03-13-2022, 10:44 AM

Quote:

Originally Posted by Gary R.

The black tank flush has never worked in our Alpine, so one day I went on a quest to find the valve.

Wasn't under the lavatory sink, as only two Pex lines are visible.

So, with advice from the folks here, I carefully removed the shower faucet, and had just a second to see the valve before it fell down to the floor behind the shower.

Given the very small access area, I decided to forget about it and reinstalled the faucet.

I would like to have a conversation with the person at the factory who decided to put it there....

Cheers!

How did the water lines completely collapse and let the valve fall to the floor? My pex lines to my valve are stiff and it just stands on it's own under the sink. Just wondering if there might be a bigger issue or ??? since you said it's never worked.

Gregory · 03-13-2022, 11:30 AM

Quote:

Originally Posted by Welshdog

Thank you Chuckster, hopefully this is the case! I had a bad leak yesterday where the black tank flush port is set in the rv wall. Took the port out and saw it was a worn cone washer, and, the water line fitting was slightly loose too. Easy fix luckily! That got me thinking about the check valve……! I’ve had to tighten several water line fittings on this rv, all were minor leaks thankfully. Prevention is way better than cure every time.
Thanks again!

Is there any reason the check valve has to be in shower wall or can I relocate it to a spot I can easily get to

Javi · 03-13-2022, 11:36 AM

Quote:

Originally Posted by sourdough

Some folks have replaced them with more robust valves and others like myself have just cut them out, placed 90s on the water lines and eliminated the whole thing. I do have hose end anti siphon valve on the inlet for the black tank flush outside in the event some kind of failure might happen. I strongly doubt that given the circumstances that would be required to siphon water back into the water supply and the fact I'm standing there the entire time.

Yep, normally the first mod I make to a new trailer as soon as I get it home...

Gary R. · 03-14-2022, 01:22 PM

Hi Danny, I did think it was odd for those stiff Pex lines to fall down, but I could see it falling sideways before it hit the interior wall or floor. I apologize for not being more clear.

I am going to borrow a borescope (or similar device) and remove the shower faucet and have a look and see where it landed. Maybe I can even hook it with a rod and pull it back up.

Spletbr · 03-20-2022, 10:10 AM

Pardon me but what does this valve do and why should I be concerned? I like to be proactive when I can!

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