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Old 11-08-2004, 08:17 AM   #1
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gray retro plumbing

I'm in the process of adding a gray tank to a '73 Tradewind just behind the rear axle between the cross members. Is there anyone out there that has a rear bath with the shower P trap that hangs below the floor and have added a tank up in between the cross members? Shouldn't the top of the gray tank be below the level of the water in the P trap? If that's the case I don't see how I can mount my gray tank up in beween the cross members against the bottom of the flooring and get enough slope from the shower P trap into the side of the tank. I DON'T want my gray water backfilling into my shower pan. I'm thinking I have to drop it at least 5 inches below the floor in order to 1) fit a 1.5" drain in to the side of the gray tank with out cutting through a cross member, and 2) get enough drain from the P trap. If I hang it low enough to what I think will be sufficient, it drops the entire tank 6 inches from where the belly pan would be normally. Is that too low to have a tank hanging down? Any insight out there?
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Old 11-08-2004, 09:10 AM   #2
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graytank drainage

tclay,

I have done the same thing in my '59, except the tank is forward of the axle.
The times you will have a problem are when the tank gets full, and while you are on the road.

Three possible solutions:

1. Install a rubber flapper valve between the shower and the tank. While this won't prevent 'seapage' past the valve, it will stop big slugs of water from backwashing into the shower as you accelerate away from a stopsign.

2. Puchase an expanding plug for the shower drain. Marine stores should have these in a size big enough for the drain. Or use a cork, with a weight to keep it in place.

3. When the tank gets full, you can always lower the front of the trailer to keep the water from flowing back into the shower. This works well if the tank is further forward.

Here is a picture of my graytank. A picture of the drain line is posted in http://www.airforums.com/forum...ad.php?t=12785, a previous thread on this topic.
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Old 11-08-2004, 12:47 PM   #3
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I haven't done this yet, but I've done a bit of planning. my setup is exactly like yours. Its ok for the tank to be above the lowest point of the trap. water "seeks its own level". since the bottom of the shower pan is above the top of the grey tank, by at least 3/4" (thickness of the floor), water will drain into the tank. even if the drain pipe doesn't enter the tank at the top.

my plan is to put a tank in the bay just forward of the shower trap. the x-members are "perforated" in the 70's trailers, so the drain can just be re-directed forward, through the x-member and into the side of the tank. when the tank gets full above this point, the shower will drain a little slow, but it will drain. showers in these trailers are fairly short events, anyway. I'll put in a 1-way flapper valve, as Don suggested, to keep anything from "sloshing" into the pan while under way...although I don't plan on driving much of any distance w/ a full tank, but you never know. it could happen...

I'd like to find a tank that is around 8" tall and a sloped bottom that terminates in the center, with a drain at the lowest point. This would be just low enough so the drain pipe runs along the outside of the belly pan, straight back to the rear of the trailer and connects the existing "exhaust" pipe. The existing sewer termination would have to be extended down several inches to accomodate this, but this seems like the most "do-able" plan, at the moment. The other option is to keep everything inside the belly pan, and tie it into the existing drains, but that would require a much smaller (22 gallon) grey tank.
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Old 11-08-2004, 02:02 PM   #4
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I have a retro-fit grey tank in my 1971 tradewind, rear bath with the P-trap going through the floor.
My tank is mounted in the location you described. It holds over 30gal, I don't recall right now what the exact amount is.
The shower drain actually enters the tank at the bottom, so does the sink drain.
It works very well now, after I added a vent line to the very top of the tank.
Your water level starts at teh shower drain, so even a slight downward slope will amake it drain just fine. Ther is a thread with my setup in it, a search will reveal it. Sorry I don't have time right now to search for you.
Before the vent was added, the tank would only fill part way, the air that was trapped would not allow more water to enter after a certain fill amount.
So, make sure you install a vent to the top of the tank, to maximize capacity and avoid having the tank hang too low.
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Old 11-08-2004, 08:31 PM   #5
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Thanks for all of your most useful advice! Here's the tentative plan: I'll tuck the gray tank (Inca Plastics H502 - 22gals) up between the cross members just behind the axle using 2" angle iron bolted to the frame. Drain the kitchen sink into it from above (under the bunk), which can also serve as a vent. The bathroom sink and shower I'll drain to the opposite end and into the side of the gray tank. The main gray drain valve will be reduced from 3" to 1.5" and drop a couple of inches and drain back along the outside of the underbelly and meet up with the retro'd black tank (Inca Plastics H367 - 21 gals) valve which will drain to the curbside and angle out to below the underbelly. What am I missing?
I'll think about this for a few days....
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Old 11-08-2004, 08:46 PM   #6
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Quote:
Originally Posted by Stormy Weather
What am I missing?
I'll think about this for a few days....
How about this: on the graytank vent, I plan to mount a tee with a screwed on cap, and bring the kitchen sink and vent line in from the side. You can remove the cap and use a dipstick to check the level in the tank.

Unless you plan to go high tech and put in level sensors. . . .

And how about tank insulation? I insulated mine by turning it upside down, covered it with 3/4" polyisocyanate (R value 5), then I overlaid the whole thing with 1/4" fiberglass.
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Old 11-08-2004, 11:06 PM   #7
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great idea! I was planning on just gauging my gray tank by how full the fresh tank was (that indicator works fine) and how full the black tank was (peering down the open toilet, not elegent I know)...but I like your idea better. As far as insulating goes, I like that idea too. Did you apply the fiberglass or is it some kind of a pan?
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Old 11-08-2004, 11:25 PM   #8
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Quote:
Originally Posted by Stormy Weather
Did you apply the fiberglass or is it some kind of a pan?
To build the fiberglass cover, I built a frame out of 2x6 the same size as the frame and crossmember opening. Positioned the tank in it upside down, with the attaching hardware. I cut sheets of foam insulation to cover the tank and taped the seams with alum foil tape, then just started brushing resin and fiberglass mat over the foam. Built up about four layers of mat, then reinforced the corners and filets with fiberglass cloth. Used about 2.5 gallons of resin and about 40 sq ft of mat and cloth. Painted it with marine paint.

Then I just popped the insulated cover off the tank, ground off the rough edges, and mounted it.

Another idea I've thought about, but probably won't do, is mount a muffin fan on the tank vent. I have two vents at opposite ends of a long tank. If I need to heat the tank a little to prevent freezing, i would just turn the fan on, and it would blow warm air through the tank and out the other vent.
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Old 11-09-2004, 09:28 AM   #9
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How does your existing black tank drain? My owner's manual lists the tank size for "landyachts (23' and 25') as "13 gallons". as far as I can tell, the bathrooms are laid out identically in our trailers. So I'm wondering how you're going to fit a 21 gallon tank in place of the 13. my tank empties in the middle of the trailer, 8" forward of the rear end. (I'll post a pic). one plan I was kicking around involved using the existing grey tank lines as drains. there are 2...one runs up along the curbside, into which the bathroom sink and shower drain. the other comes back along the street side of the trailer. either or both of these could be fitted to the grey tank, and all plumbing could be kept inside of the belly of the trailer. There would be very little slope, if any, but I figure that's what the tounge jack is for.

to go "outside the belly pan" would be more complicated, as an outside drain pipe going toward the rear streetside corner would interfere w/ my BAL stabilizer jacks. it could be done, I think...but it would also require a 3" drain pipe running over from the existing tank drain, 4' away. and because of a frame extension on my trailer, would require it to hang down rather low.

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Old 11-09-2004, 08:35 PM   #10
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Chuck, I can't tell you how long I've stared at that diagram in my manual! My new black tank will be in the same location of the old one however it will hang below the floor 5 inches. I'll support in underneath with two 2" angle iron bolted to the frame, horizontal to the other cross members. I'll also strap it perpendicularly with a couple of 1 inch 1/8" steel U shaped straps. I'll also have to build a plywood box to support the toilet as this tank won't support the weight of the user as the old one did.

The black tank will drain curb side. I'll meet that up with the gray drain pipe where the new waste dump valve will be. Thanks for reminding me of the leveling jacks...I totally for got about those as I've removed them when I removed my belly pan....I'm going to have to rethink the location of the gray drain pipe. Here's my delemma: the deepest part of the gray tank is 6 inches. That's right about where the bottom of where the cross members align....hmmm. Maybe I'll have to have two dump valves. The gray one would have to be were the tank would be sitting....I can't remember if there's a wheel in the way. I'm going to have think about this a bit more.

That's what I love about this forum....keeps us all from being stupid! Thanks Chuck!
Tom
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Old 11-10-2004, 10:30 AM   #11
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I think you can have both drains terminate in the same spot like you described, but it may have to hang a bit lower than you originally thought, to allow for the stabilizing jacks. The grey tank drain line will start from the tank, heading back toward the back corner of the trailer along the inside of the streetside frame member, but it will have to re-directed to the outside of the frame member with a couple of elbows. On my trailer, there is a gap between the spot where the axle mounting plate ends, and the frame extension begins. that's where I'd put the transition. Then it can continue the rest of the way to the corner, hanging along this outer edge of the trailer, under the "banana wrap", and it'll just have to be suspended down an inch or two to allow for the jack's screw.

(I don't know what purpose that frame extension serves...the only thing I can see is that it gives you some place to mount the fresh water intake pipe; other than that, I'm kind of to its purpose. there's already a hole cut in it to allow that jack screw to come through.)

The thing that concerns me about your proposed black tank, though, is that there may be structural issues to address. The trailer's structual integrity comes from multiple sources working together as a unit; the shell, (inner and outer skin), the plywood floor, and the steel frame all work together. Compromising any one of them could significantly weaken the structure as a whole. The plywood floor is a major component, here, and I wonder what cutting such a large hole in it would do. that's alot of material to remove, and very close (like, and inch? maybe 2?) from the rear of the trailer. The larger units had tanks under the floor, but they were completely under the floor, and only needed a 3" round hole cut in the plywood to mount the toilet.

Then there's the "rear end seperation" issues on the longer trailers of that era...I'm not sure if it was a problem w/ '73's and before, as they had no grey tanks to add extra weight...but you ARE talking about having a grey tank, as well, which must be suspended from the frame. And the even heavier black tank will also be supported directly by the frame, and have a 6 foot lever arm from its position to the rear axles to magnify that force. The thing about having it under the floor and resting directly on the frame is that this will tend to pull the frame down from the plywood floor and shell. The original tank sits ON the floor, which is going to have a tendancy to force the shell/floor down to the frame, thereby helping to hold things together.

I'm not an engineer, and I may be totally off base, here. But it seems to me that in order to do what you're proposing, you'll need to do some sort of reinforcement of the frame to compensate for the areas where you'll be weakening the structure. I don't know what, or how much would be required, though. the angle-iron supports will add some strength, but it may not be enough. Then again, it might be fine, just as long as you don't drive down the road with the tanks full...never camp anywhere there isn't a dumpstation nearby.

just something to keep in mind
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Old 11-10-2004, 03:32 PM   #12
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Grey plumbing pics

here is a series of pics from my grey tank install.
i have since re-doneit, but not drastically. I had to re-route the shower pipe to accomodate my stabilizers....when I did my bathroom floor revamp.
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Old 11-10-2004, 08:25 PM   #13
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Chuck, I have that same frame extension on my Tradewind and wondered the same thing. I thought the PO welded it there for backend support. I'm thinking of doing the same thing to the other side. I too share your concerns about the load, but I don't know how else to get bigger black tank. I think I'll take my chances, not travel with a full tank, and just watch for problems. Next Fall I'll probably be kicking myself and saying that I should have listened to that Red Sox fan! (Amazing playoffs/series btw)

Uwe, thanks for the pics. Helps me see what below the belly plumbing might look like....not bad at all.

I'll post pics of my progress when I get around to it. Thanks guys!
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Old 11-11-2004, 08:59 AM   #14
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yeah, how about those Red Sox, eh??

I think what you're proposing is very "do-able"...and I may just have to steal your ideas for myself. I'm just saying that we should both plan on reinforceing to compensate for any weakness we might create. exactly what or how, I don't know. I'm not even sure who WOULD know. an engineer of some sort, perhaps? I do know that I can put a window into just about any wall in my house, where there has never been one before, even though it would remove the support of one or more studs that are holding up the house. The proper methods of compensating for this loss of structural strength in one spot, by transferring loads to another are in the building codes, and are known to just about any carpenter. So all we have to figure out is "who is the travel trailer equivalent of a licensed carpenter?"

oh, btw: post some diagrams of how you intend to mount/support the black tank!
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