Black tank plumbing question - Montana Owners Club

gwsmith1 · 07-12-2018, 03:15 PM

I have searched high and low, and while there is a ton of good information out there, I still have not found the answer to my question(s)..... I have a 2005 Montana 3670RL. My first question is is it possible that the black tank system does NOT have an Air Admittance Valve ? I have found the one for under the kitchen cabinets (presumably for the galley tank) and the one under the shower base (definitely for the grey tank), but have been unable to locate one for the black tank. I have read that they could be hiding in the wall of the pantry (btw there are no access panels in the pantry),but since the rig is at the lake and I am at the office I thought I could toss the question out. Mine does have the washer/dryer hookups that drain into the black tank (if that matters)but tracing the drain lines from the underbelly to where they terminate I have not been able to locate one.

Secondly, my black tank flush is no longer working, as well. I have read over and over that there is an anti-siphon valve under the bathroom sink, but have searched, again, to no avail. Both the cold and hot supply lines come straight out of the floor and up to the faucet. Looking underneath (in the basement) I have not found it, either, unless I just don't know what I am looking for. Any suggestions ?

Thanks in advance for the help !

Montana Man · 07-12-2018, 03:37 PM

Under the bathroom sink, are there two white water lines? They would be in addition to the red and blue lines to the faucet.

jimcol · 07-12-2018, 04:01 PM

You don't have an air admittance valve for your black tank. You have a vent pipe that goes up through the wall and exits the roof. I believe it is a two inch but not sure. I have two on my roof. One for the black tank and one for the grey. From the roof your nose will up you determine which is which. The galley tank uses the valve to vent the tank. My anti siphon valve is in the wall between the shower and storage closet immediate inside the door. Mine has a cover on the back wall of the closet to get to the valve but many reported they had to cut the back wall to find the valve.

**Carl n Susan** · 07-12-2018, 04:10 PM

Listen to Jimcol, he is spot on. A Search of this site should uncover pictures (from Steve Reigle and someone else (BB_TX?)) of finding and accessing the anti-siphon valve behind the shower.

**AZ Traveler** · 07-12-2018, 04:33 PM

gw,

Welcome to the forum!

The other way to flush the black tank is to bring a hose with sprayer head made to flush into your bathroom.

cpaulsen · 07-12-2018, 05:12 PM

The 3670rl I had.......the anti-siphon valve was under the bathroom sink.

BB_TX · 07-12-2018, 07:51 PM

I don’t know the floorplan of that model. On mine I can remove a panel in the basement and see the underside of the floor under the shower. There are 4 water lines going up into the back wall of the shower, 1 red, 1 blue, and 2 white. Shower valve only needed the red and blue. That told me the black tank flush anti siphon valve was up in that same wall between the shower and my entry closet. I had to cut a new opening in the back wall of the closet to access it. The existing opening was in the wrong place. I could reach in and feel it but not access it.

BuilderBob · 07-12-2018, 09:28 PM

Welcome to the MOC family from Washington St! The black tank vents out the roof.

gwsmith1 · 07-13-2018, 01:47 PM

Firstly, thanks to everyone for all of the quick help....

MontanaMan.... I only have 2 lines (pex...one is white and the other is reddish) that are under the sink. They are the supply lines to the bathroom faucet.

I will follow the advice and do some investigation around the shower/closet area to see what I find!

Thanks again.

Montana Man · 07-13-2018, 01:59 PM

OK, keep looking you'll find it. Good luck.

jeffba · 07-13-2018, 03:40 PM

you may be able to see them if you remove the back wall of the basement and follow them up from there.

cpaulsen · 07-13-2018, 05:08 PM

Like I said.........the valve is under the bathroom sink. I had a 3670RL and that is where mne was......I changed it....that is how I know.

RRman · 07-25-2018, 02:25 PM

My 05 3670 Big Sky has a anti-siphon valve under the bathroom sink, presumably for the flusher or outside shower (?)

I'm getting ready to replace my Black Tank. The Flusher is centered on the "back" wall of the tank (opposite the deep end). I hope to re-use it.

Ed and Carole · 07-25-2018, 02:31 PM

2008 3400 our anti-siphon valve is behind the shower and to access it there is a plastic cover in the tall wall cabinet in the kitchen. This is also the space with the sliding door which isolates the bedroom and main living area. The black tank vents only on the roof.

Jcroome · 07-25-2018, 03:15 PM

Wouldn't it be nice if the manuf. provided a good owners manual and online schematics for electrical and plumbing, etc. by models/floor plan? Could be done by serial numbers for changes. Almost every other vehicles manuf. do that. It would reduce the questions on forums and wasted time by ? 50%. Just Saying!!!

MrMeeks · 07-25-2018, 04:32 PM

I've had a similar problem locating the sewer anti siphon valve. But alas, i found it. It's on the wall behind the shower fixture for our 2955RL. Check top cupboard for access panel, but be sure to close pocket door or you'll never find it. It should be there. Just don't drop your flashlight down there like I did. Good luck.

Lee & Ruth · 07-25-2018, 05:59 PM

I totally agree! As much as these things cost, they should provide a DVD that shows owners how things work and how to make repairs. The owners manual is worthless.

h2ojocky · 07-25-2018, 11:10 PM

MrMeeks what year is your 2955RL? Mine is a 2005 and when I looked behind the panel I don't remember seeing anything. I did not close the pocket door though, I will have to try that!

BB_TX · 07-26-2018, 09:10 AM

I believe the 2955RL is basically the same as my 3075RL. My valve was also in the wall between the shower and the entry way closet/cubby/shelves in the pocket door area. You can see in the first picture where the factory cutout with plastic cover is located. And you can see that the anti siphon/vacuum breaker valve is located. I could reach in the original opening and feel the valve, but could not reach it. Had to cut a new opening to access the valve. I just removed it and replumbed the lines and use and external anti siphon valve.

Pocket door had to be pulled out to see that area.

I looked in the basement under the shower floor (had to remove one panel) and saw 4 water lines going up. Shower only needed the two. So I knew the two extra ones were for the anti siphon valve in the wall.

Made a picture frame around the piece I cutout and used that for a cover for the new opening.

routemaster · 07-26-2018, 10:27 AM

Quote:

Originally Posted by gwsmith1

I have searched high and low, and while there is a ton of good information out there, I still have not found the answer to my question(s)..... I have a 2005 Montana 3670RL. My first question is is it possible that the black tank system does NOT have an Air Admittance Valve ? I have found the one for under the kitchen cabinets (presumably for the galley tank) and the one under the shower base (definitely for the grey tank), but have been unable to locate one for the black tank. I have read that they could be hiding in the wall of the pantry (btw there are no access panels in the pantry),but since the rig is at the lake and I am at the office I thought I could toss the question out. Mine does have the washer/dryer hookups that drain into the black tank (if that matters)but tracing the drain lines from the underbelly to where they terminate I have not been able to locate one.

Secondly, my black tank flush is no longer working, as well. I have read over and over that there is an anti-siphon valve under the bathroom sink, but have searched, again, to no avail. Both the cold and hot supply lines come straight out of the floor and up to the faucet. Looking underneath (in the basement) I have not found it, either, unless I just don't know what I am looking for. Any suggestions ?

Thanks in advance for the help !

Mine is behind the shower taps it is to give hight I belive, you will need small hands to reach it.The spray unit in tank can also clog up.
Den.

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