locating black tank anti backflow valve in my 3813 - Montana Owners Club

scuba dude · 03-02-2022, 05:41 PM

Any one know where the black tank anti backflow valve is in a 2020 3813MS. I have looked under bathroom sink. Behind drawers in washer, dryer closet in hall. I would like to change it before it starts leaking but gotta find it first.

Mikendebbie · 03-02-2022, 06:11 PM

Just a thought…I think the backflow valve has to be located higher than your toilet. Have you looked for an access panel on the wall of the wardrobe behind the toilet?

rohrmann · 03-02-2022, 06:37 PM

Looking at the floorplan, I would guess it could be in the wall between the coat closet and the shower. On our rig, it's located in a similar location, but between the shower and the pantry. We have a pocket door in that wall, so it's at least visible. On a positive note, I have been using the black tank flush weekly since we purchased the rig and we full time in it, and the valve has never failed.

scuba dude · 03-03-2022, 06:38 AM

No luck locating yet, not under sink or no access panel that I can locate in a wall. Beginning to wonder if it may be behind the basement wall that is removeable to access everything under floor in basement directly beside wetbay.

BB_TX · 03-03-2022, 08:25 AM

If can look in the basement and see under the bathroom area you might see water pipes for the lavatory, shower, and toilet plus two extra white water pipes going up that don't really seem to be have a purpose. You may have to remove a panel or two to see that area. Likely the valve is in one of those walls and that might tell you which one.

rohrmann · 03-03-2022, 12:50 PM

Quote:

Originally Posted by scuba dude

No luck locating yet, not under sink or no access panel that I can locate in a wall. Beginning to wonder if it may be behind the basement wall that is removeable to access everything under floor in basement directly beside wetbay.

It's not going to be at the basement level. Like was said, it will be located above the level of the toilet rim. That's the only way it could prevent backflow from the black tank. https://www.recpro.com/rv-vacuum-bre...571-vac-chk-a/

scuba dude · 03-03-2022, 05:54 PM

I placed a call to RV station where I purchased the camper and talked to a service tech that I knew was pretty sharp and he said he thought it was in the wall behind the shower control lever. I can only hope it's that simple. I will update later, Thanks for the help.

BB_TX · 03-03-2022, 06:19 PM

Look inside your coat closet for an access panel in the back, especially if your shower controls are on that wall. Mine was in my wall between my shower and my entry/coat closet. And there was an access panel on the back wall of the closet. Alas, it was located in the wrong place.

I could reach in and feel the valve but not access it. I had to cut a new access opening at the location of the valve. And again, if you can see that area in the basement and see 4 water pipes going up thru the floor then it is likely 2 for the shower and 2 for the flush valve.

I eliminated that valve and used an external anti siphon valve.

scuba dude · 03-04-2022, 06:44 AM

I checked the closet and no excess there. What rv tech told me made sense because the shower control lever mounts to a larger hole cover that mounts to the shower wall. Just hope if it is there that it's easy to get to.

BB_TX · 03-04-2022, 08:28 AM

Hopefully that panel will give you access. If you can see the valve but can not reach it to take it out, with careful measurements you can probably cut an access in the back of the closet. I cut out a square opening at the valve location and then made a picture frame to use the cut out piece for the cover.

First picture shows the original factory panel and, below it, the opening I had to cut to access the valve. Second picture shows the cover I made to close the opening.

twindman · 03-04-2022, 12:57 PM

If you have to start butting holes in the wall, I would find the hoses in the basement behind the wall and just cut them off and loop them together. Then use an external valve if you feel the need. I don't use one because I always hook up the hose, back flush the tank, and turn off the hose. No way anything can feed back into the system.

scuba dude · 03-05-2022, 08:38 AM

Thanks, I like your idea. Much better than cutting holes.

BB_TX · 03-05-2022, 01:37 PM

Quote:

Originally Posted by scuba dude

Thanks, I like your idea. Much better than cutting holes.

I agree. By eliminating the valve you no longer need the raised loop for the anti siphon/vacuum breaker valve to work properly. Just make sure you are cutting the correct pipes. If you look at the pictures I posted above you can see the pipes look pink. That is because they were winterized at the time. If your pipes are white opaque like mine you can pump antifreeze thru the flush port and see which pipes turn pink in your basement. Or you may have a red pipe, blue pipe, and two white pipes going up together below the shower. In that case they would be hot, cold, and (most likely) two flush pipes. All mine were white.

In my case I could see the pipes in my basement but could not easily access them. Choice was the closet or open up the belly. I chose the closet.

bcrvman · 03-09-2022, 04:58 PM

Quote:

Originally Posted by scuba dude

Any one know where the black tank anti backflow valve is in a 2020 3813MS. I have looked under bathroom sink. Behind drawers in washer, dryer closet in hall. I would like to change it before it starts leaking but gotta find it first.

Looks similar to my 3811, it's likely in the coat closet at the bottom will be an access hatch. I found it impossible to work in so cut a hole on the other side. Will cover with a picture frame. I doubt anyone will notice though, that area is normally covered with a jacket.

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