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Old 04-14-2021, 04:41 AM   #1
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Brand: Thor Motor Coach
Model: 28Z
State: California
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THOR #22842
Extra Gray Water Valve

Hello all...total newbie and just took delivery on my used 2020 Four Winds 28z on Sunday. While doing my check out walk through I saw a valve handle under driver side that made no sense. I asked sales woman about it and she said it is extra gray water valve. When asked why she said some models have it and some don't. While I realized the inadequacy of that response I also realized she had no clue. She said my friend (who had just signed on a 28A) did not have that valve.

So now I must task you all with why is this valve there? it is not an actual drain but likely cuts off shower and vanity sink (I know this as first use of vanity it would not drain and after much consternation a fizzing light bulb went of and I kind of remembered the valve). I just do not get the purpose of it if other coach's with same (or similar) configuration do not have it. I hope that one of you wizards can impart some knowledge on this! Thanks!

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Old 04-14-2021, 11:12 AM   #2
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Quote:
Originally Posted by Lawgeek View Post
Hello all...total newbie and just took delivery on my used 2020 Four Winds 28z on Sunday. While doing my check out walk through I saw a valve handle under driver side that made no sense. I asked sales woman about it and she said it is extra gray water valve. When asked why she said some models have it and some don't. While I realized the inadequacy of that response I also realized she had no clue. She said my friend (who had just signed on a 28A) did not have that valve.

So now I must task you all with why is this valve there? it is not an actual drain but likely cuts off shower and vanity sink (I know this as first use of vanity it would not drain and after much consternation a fizzing light bulb went of and I kind of remembered the valve). I just do not get the purpose of it if other coach's with same (or similar) configuration do not have it. I hope that one of you wizards can impart some knowledge on this! Thanks!
Just a wild guess but maybe the floor plan necessitated two smaller gray tanks instead of one larger gray tank.

Bob
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Old 04-14-2021, 11:41 AM   #3
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Go to the Owners Resource site and register. You will then be able to downlaod the schematics for your coach.

https://www.thormotorcoach.com/owners/

Without pictures it is hard to help but I will throw this out there...... I had an Outlaw 29H and it had two black tank valves. The black tank was on the paseenger side and the grey tank was on the drivers side. I think there were two reasons for two valves.

The blank tank drain plumbing ran under the drive shaft and over to the grey tank where they merged for draining. There was a valve right at the bottom of the tank and then one on the drivers side for draining. The valve at the tank being closed kept debris from filling the plumbing and potentially clogging. It also allowed the blank tank to be closed if the plumbing got ripped off the bottom of the coach. It was about 6" off thr ground at best.

I ended up removing the black tank drain that went under the drive shft and added a drain for it on the passenger side as a result because I knew some day a speed bump or debris in the road would tear it off.
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Old 04-14-2021, 12:02 PM   #4
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I was thinking the same thing... but this extra valve is on the driver's side...
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Old 04-14-2021, 01:41 PM   #5
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Where, on the driver's side, would this "extra" valve be?

I can see, with your floor plan, that the black tank is likely under the passenger side and probably has an isolation valve there in addition to the black and grey isolation valves on the driver's side used for dumping. I can see no use for an extra grey isolation valve on either side of the coach.



EDIT: Further research shows a single grey water isolation valve directly below the grey water tank.

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Old 04-14-2021, 01:43 PM   #6
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I think Judge has your answer.
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Old 04-14-2021, 02:20 PM   #7
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I think Judge has your answer.
If we assume that the O.P. just got the side of the RV a bit confused: I agree.
That does seem like a setup that could use the extra Blackwater tank valve.
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Old 04-15-2021, 05:09 AM   #8
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My Bad

OP got the wrong side lol. Dump valves are on driver's side. This valve is on passenger side below the head. I wonder if it is to prevent back flow from tank into shower during transit? The shower is a low point that may be close to same height of tank. Assuming there is not a check valve at tank, this would help prevent back flow??? Sounds plausible to me but I really know very little lol.
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Old 04-15-2021, 10:36 AM   #9
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No problem...
We have decided that valve is sort of an "emergency prevention procedure".
Since the cross-tube rides so low across the underbelly of the RV: It would keep the tank from being drained unexpectadly; should that tube get busted.
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Old 04-15-2021, 02:32 PM   #10
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Quote:
Originally Posted by Lawgeek View Post
OP got the wrong side lol. Dump valves are on driver's side. This valve is on passenger side below the head. I wonder if it is to prevent back flow from tank into shower during transit? The shower is a low point that may be close to same height of tank. Assuming there is not a check valve at tank, this would help prevent back flow??? Sounds plausible to me but I really know very little lol.
It has nothing to do with the shower. It is a BLACK tank isolation valve, not grey tank isolation valve.
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Old 04-16-2021, 02:57 PM   #11
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Thank you all

Thanks for the thoughts and opinions. I reviewed the schematic and it does show a valve right at the BW tank. It makes total sense that this would be a backup to prevent draining the tank should one break the low lying pipe. I thought it was gray water as it seemed like it was a small valve, but I really did not get a good look. I'll confirm later today when I pick rig up from storage.

I really have to give props to Thor for the online resources. I actually signed up and put my VIN in the day I put a deposit down on the rig. It is nice having every manual and schematic at your fingertips!

I appreciate you all for indulging and tolerating my newbyness! I am sure I will have many more questions to come and may even end up in the "they sell these things to anyone nowadays" category! Thanks!
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Old 04-16-2021, 06:14 PM   #12
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" Newbyness" got to ad that to the RV data base
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Old 04-17-2021, 02:09 PM   #13
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I have the Chateau 28Z. On the drivers side there are 2 valves, Small one is grey and the other larger one is Black. Now on the passenger side there is another Valve for the same black tank. It's there just in case the black water line that goes under the drive shaft gets hit, the waste water does not spill out on the ground. I ALWAYS keep that one off while driving. I also keep it off when camping. I use it as (Extra room) so when the black tank gets full I open the valve on the passenger side and I get more room as it fills the long pipe up. That said, I have been in some areas with limited ground clearance and have not had any problems. I do keep a rubber coupling just in case to make repairs. But I also keep a couple sections of PEX, fittings and crimper just in case. (was a Boy Scout Leader)
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Old 04-17-2021, 02:49 PM   #14
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THOR #22388
Here are ALL the Diagrams for the 28Z.
See page 17.
Attached Files
File Type: pdf Chateau-Four Winds_28Z_diagrams .pdf (2.95 MB, 166 views)
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Old 04-17-2021, 02:58 PM   #15
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This is the spare coupling I keep on hand.

https://www.lowes.com/pd/Fernco-3-in...ing/1000075327
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Old 04-19-2021, 04:32 AM   #16
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Quote:
Originally Posted by CHS View Post
I have the Chateau 28Z. On the drivers side there are 2 valves, Small one is grey and the other larger one is Black. Now on the passenger side there is another Valve for the same black tank. It's there just in case the black water line that goes under the drive shaft gets hit, the waste water does not spill out on the ground. I ALWAYS keep that one off while driving. I also keep it off when camping. I use it as (Extra room) so when the black tank gets full I open the valve on the passenger side and I get more room as it fills the long pipe up. That said, I have been in some areas with limited ground clearance and have not had any problems. I do keep a rubber coupling just in case to make repairs. But I also keep a couple sections of PEX, fittings and crimper just in case. (was a Boy Scout Leader)
Thanks CHS! Great idea to carry a coupler or two just in case. I will do that.
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Old 04-20-2021, 12:38 AM   #17
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THOR #2812
Another discussion on that crossover black tank drain, mentioned: valve at tank was to keep crossover empty in cold weather. A full, frozen crossover could be a problem.
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Old 04-20-2021, 01:04 AM   #18
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And messy: if it cracks open...
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Old 04-20-2021, 02:42 AM   #19
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I was told the “extra” valve was there because the “solids” in the black tank will settle to the low point and you want them to remain in the tank instead of possibly packing the pipe full of disgusting ick.
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Old 04-21-2021, 06:20 PM   #20
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Weight of “Ick”

Quote:
Originally Posted by Pete'sMH View Post
I was told the “extra” valve was there because the “solids” in the black tank will settle to the low point and you want them to remain in the tank instead of possibly packing the pipe full of disgusting ick.
That’s why I keep that valve closed until it’s dump time. That “ick” could add a lot of weight to the piping crossing over to the dump side. Our 2000 Hurricane has a 4” crossover from the black tank, routed around the gas tank to the dump valve. If I leave the “extra” valve open on the passenger side, it will fill with “ick”y liquid to the tune of about 80 lbs of weight. That just adds to the aggravation if it settles and clogs.
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