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Old 07-20-2004, 06:15 PM   #1
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Combined Gray and Black Water?

I have been thinking about reworking the holding tanks on my 1973 31' Sovereign mid-bath. The current black water tank is above the floor and the gray water tank is a poorly added addition made by a PO (bad size, wrong location, and has a crack in it). I read some of the threads dealing with gray tank additions and with macerator pumps. Somewhere in the threads I also saw something mentioned about newer AS's having a combined tank and that got me to wondering...

So here is a proposal that I would appreciate feedback regarding:

1.) Remove both of the existing tanks.
2.) Add a single holding tank under the floor in a location below the toilet.
3.) Use the single tank for black and gray water.
4.) Add a macerator pump to drain the tank.

The single tank might only be 20 to 25 gallons. I understand that this would be a limitation for boondocking. It seems like it would still be a lot better than no gray water tank at all. I also understand that I would have to drain the tank at periodic intervals rather than being able to drain the gray water all the time if I am hooked up to the sewer system at a camp ground. This does not seem too limiting as long as I have a good tank sensor so I know when this is necessary. It seemed to me that using the macerator would make the options for where I could drain a bit broader as well.

So some questions in my mind are:

1.) Does the overall approach seem reasonable?
2.) Does anyone have any ideas on how I could fit in a larger single tank? I could let a larger tank hang down further I guess but I am not sure I want to do that - what do you think?
3.) Are there any other down sides to using a single tank for both other than perhaps the size issue?
4.) Is there any potential for problems with the shower draining properly? That would be the lowest drain in the system of course. Can I still get to a nearly full tank without the shower back flowing?

Thanks in advance for the help,

Malcolm
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Old 07-20-2004, 06:37 PM   #2
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Quote:
Originally Posted by malconium
I have been thinking about reworking the holding tanks on my 1973 31' Sovereign mid-bath. The current black water tank is above the floor and the gray water tank is a poorly added addition made by a PO (bad size, wrong location, and has a crack in it). I read some of the threads dealing with gray tank additions and with macerator pumps. Somewhere in the threads I also saw something mentioned about newer AS's having a combined tank and that got me to wondering...

So here is a proposal that I would appreciate feedback regarding:

1.) Remove both of the existing tanks.
2.) Add a single holding tank under the floor in a location below the toilet.
3.) Use the single tank for black and gray water.
4.) Add a macerator pump to drain the tank.

The single tank might only be 20 to 25 gallons. I understand that this would be a limitation for boondocking. It seems like it would still be a lot better than no gray water tank at all. I also understand that I would have to drain the tank at periodic intervals rather than being able to drain the gray water all the time if I am hooked up to the sewer system at a camp ground. This does not seem too limiting as long as I have a good tank sensor so I know when this is necessary. It seemed to me that using the macerator would make the options for where I could drain a bit broader as well.

So some questions in my mind are:

1.) Does the overall approach seem reasonable?
2.) Does anyone have any ideas on how I could fit in a larger single tank? I could let a larger tank hang down further I guess but I am not sure I want to do that - what do you think?
3.) Are there any other down sides to using a single tank for both other than perhaps the size issue?
4.) Is there any potential for problems with the shower draining properly? That would be the lowest drain in the system of course. Can I still get to a nearly full tank without the shower back flowing?

Thanks in advance for the help,

Malcolm
Malcolm,
I think it's feasible, but am wondering why you would want to get rif of the existing black tank? 20 gal for grey and black combined is definitely too small.
To add a sizeable grey tank, you just need to remove the existing one that you don't like, and take a look at the framework behind the rear axle. The grey tank should be as close as possible to the rear axle. ou might have to remove one crossmember, and beef up the frame and remaining 2 cross members, but this way you can add a 40+ gal grey tank that barely protrudes under the trailer. I am doing this to my 1963 Overlander.
You might be able to do a size of 54 wide, by 43 long, tapered in depth from 5in to 7in., with teh 2.5in drain on the lowest side.This would hold close to 60gal.
Make sure and add a vent, so the tank can fill all the way, and drain easily.

2) seems reasonable, if the grey/black combo tank is large enough
3) well, you can often drain grey water without much dismay. Not so when there's black content. If you're getting too full, black might backwash into the shower pan.
4) Depends on the installation. The shower will be 1 or so inch higher than the top of the tank, and it can feed into the grey tank just fine, at least it does so on my 71 Tradewind. If, however, you overfill the combo tank, then gross things might end up in the shower. ( Repeat of your 3rd question)

I've come to the conclusion over time, that it's best to have the fluids separated.
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Old 07-20-2004, 06:45 PM   #3
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Frame change...

Uwe,

Thanks for the comments. I could visualize removing one of the cross members and re-enforcing the two remaining ones, but what are you doing for supporting the plywood floor in the middle of the roughly 4' x 5' area over the new tank? How are you intending to support the tank itself? I have noticed that a lot of tanks appear to have an overhang along their top edges that suggest they can be hung from the top. Is that true or must they typically be fully supported from the bottom?

Malcolm
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Old 07-20-2004, 06:51 PM   #4
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Why remove the black tank?

Uwe,

I forgot to mention that my main motivation for wanting to remove the above floor black tank has to do with possible floor plan changes I am contemplating. The black water tank on my unit is partly in the back bedroom. In the original layout it was covered by the bedside cabinet next to the cross-wise bed. Since my unit was almost entirely gutted when I got it I have the option of changing things around a bit. I have to build whatever I build from scratch so I might as well consider my options before I jump in. I need a new toilet too. The old one was shorter so it would fit on top of the bw tank. I could install a somewhat more convetional looking unit it if mounted to the floor instead of 8 or so inches up in the air.

Malcolm
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Old 07-20-2004, 10:44 PM   #5
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Quote:
Originally Posted by malconium
Uwe,

Thanks for the comments. I could visualize removing one of the cross members and re-enforcing the two remaining ones, but what are you doing for supporting the plywood floor in the middle of the roughly 4' x 5' area over the new tank? How are you intending to support the tank itself? I have noticed that a lot of tanks appear to have an overhang along their top edges that suggest they can be hung from the top. Is that true or must they typically be fully supported from the bottom?

Malcolm
Malcolm,
I used 4in flat stock, 3/16in thick and welded it on the open C-Channel main frame, and also on the crossmembers fore and aft of the future tank.
If your main frame rails are already boxed in, then you might not need to re-inforce with flat stock.
Tank support:
2x2 1/8in angle stock, welded to the frame and cross members to front, and sides will make a 3-sided cradle for the tank. Make sure the angel protrudes about 1.25 in down from the frame and cross members.
Leave the rear open, do not weld the rear section inplace.
Now you can put the tank in place, brace it up, and slide a fitting sheet of plywood in the frame, remove the braces and insert the plywood all the way. Now your tank sits on plywood, supported on 3-sides so far.
Make provisions so you can bolt the 4th piece of plywood to the rear of the new tank framework. This removeable piece will allow you to r/r the tank anytime you need to, for service and to repair troubled plumbing etc. Your tank can be roughly 4.5in tall, 43 in wide and 54 inches long. Makes for a 45gal or so grey tank, not shabby. Much like new trailers.
The frame work for the tank, if welded properly, will also add reinforcement to the frame rails, offsetting some of the extra stress on the frame. Make sure it goes immediately behind the rear axle, not way out back somewhere. It will take some fabricating, and I hope that this will not be above what your willing and able to do. Use your best judgement, it's not very difficult, just tedious. A black tank could possibly mounted in a similar fashion, but I am unfamilliar with your trailer's layout. Usually the trouble with black tanks is that the frame gets in the way of sub-floor mounting, unless it's a rear bath.
A grey tank will work fine with a 1.5in drainpipe. You will have to adapt the plumbing to accomodate a grey valve and the piping for it. And don't forget the venting system.
I'll show you my installation once it's done.
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Old 07-20-2004, 10:47 PM   #6
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Quote:
Originally Posted by malconium
Uwe,

I forgot to mention that my main motivation for wanting to remove the above floor black tank has to do with possible floor plan changes I am contemplating. The black water tank on my unit is partly in the back bedroom. In the original layout it was covered by the bedside cabinet next to the cross-wise bed. Since my unit was almost entirely gutted when I got it I have the option of changing things around a bit. I have to build whatever I build from scratch so I might as well consider my options before I jump in. I need a new toilet too. The old one was shorter so it would fit on top of the bw tank. I could install a somewhat more convetional looking unit it if mounted to the floor instead of 8 or so inches up in the air.

Malcolm
Most quality toilets come in tall and low sizes, makes little difference to me, actually. I use a low profile Sea-Land in the Tradewind, and it works great for me. I got it from www.rvpartsoutlet.com
In your case, my guess is that the frame is in the way of sinking the tank under the floor, in the current location of the toilet.
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Old 07-21-2004, 09:18 AM   #7
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I like Uwe's idea...almost decided on that one, myself, by my trailer is too short to do that. it would probably work fine on yours. the problem with mine is that there isn't 4' of unobstructed space behind the tank. my stabilizer jacks and sewer outlet would interfere, so you couldn't slide a long sheet of plywood in there. But otherwise...this is the same setup as the fresh water tank. I'm still trying to decide if I want to do a "half-size" version, which would work, or go "outside the belly pan" and have a deeper tank, which would require plumbing below the belly pan level. decisions, decisions....

If you only used one frame bay, without removing any x-members, there'd be room for about a 24 gallon tank. (http://www.watertanks.com/calc.asp).

IMO, a single tank of 25 gallons would NOT be good, and NOT better than no grey tank at all. I just came back from a weekend of dry camping on private property...no problem to just let the grey water go on the ground. there are still situations where this can be very handy. I brought the black tank contents home with me, and used my blue-boy to shuttle it into the back yard, where I could access a basement window that just happens to be right above a clean-out for my septic tank. used "the Sewer Solution" (poor man's macerator) to pump out the blue-boy.

even if I had a grey tank, and couldn't have dumped it where we were staying, I would have been able to bring that home, too...and then just dump it in the driveway. a single, combined tank would have meant many, many trips back and forth w/ the blue boy.

I suppose a macerator pump (ka-ching!) would solve this...but a single tank would still be a limiting thing. I'm sure there are plenty of situations where you might have a water hookup, AND be able to dump grey water, and in such cases, your wash water use would be unlimited. not so w/ a combined tank.
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Old 07-21-2004, 11:36 AM   #8
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Chuck,
The black plumbing on your Safari would have to be changed. The levelors can be re-installed after the grey tank system is in place, you just need to install a stringer for the inner bolts. All teh weight is supported by the bracket that bolts to the frame rails. Also, using one x-member space, and going deeper is ok, just look at the new traiilers, lotsa stuff protruding down low, especially on the 22 models.
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Old 07-21-2004, 12:29 PM   #9
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Support in the middle of the tank?

Uwe,

I think I understand all that you said about your tank installation. I still do not know how you are supporting the center of the plywood floor that is in the middle of the 4' x 5' cavity however. Is the tank itself helping with this?

Also can you tell me where you got the tank?

Thanks,

Malcolm
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Old 07-21-2004, 12:51 PM   #10
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Malcom: take a look at the fresh water tank diagrams in the service manual. the only thing holding it up in the middle is the plywood floor...I believe its marked as 1" thick...that would be pretty strong, even when only suspended from its edges by those "z angle" brackets.

Uve: I wouldn't have to change the black tank plumbing if I stay "inside the pan" my black tank sits on the floor, and empties straight down. there is a 6" long "t-wye" type adapter that goes from the dump valve straight down and sticks out of the belly pan just enough to get a slinky on it. the center of this pipe is about 8" forward of the rear-most x-member, right in the center. the grey pipes enter from the sides (parallel with the bumper), then curve 90 degrees and head forward along the inside of the main frame rails...the one on the street side goes all the way to the galley. the one on the curb side only goes a couple of feet forward, and hangs a hard left over to the shower. My idea is to basically put a tank between the galley and the existing drain outlets, using the same drain pipes that are there now. The long drain line that goes to the galley pops up through the floor just behind the wheel well, and is hidden under one of the bunks; that would empty into the top of the gray tank. This will drain the galley, as well as vent the tank. then the rest of the drain pipe will just attach to the side of the tank, facing aft...the dump valve will go at the end of the pipe, just before it connects to the existing "collector" fitting. the handle can stick out into the bumper compartment, right next to the existing black dump valve handle, or it could go straight down through the pan. the shower drain just needs to be turned around and connected to another inlet in the tank. the bathroom lav's drain would attach to the other end of the tank over near the curb side.

one of these days, I'm gonna learn to use this nifty 3-d rendering program we have, and post a pic.
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Old 07-21-2004, 01:15 PM   #11
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Quote:
Originally Posted by malconium
Uwe,

I think I understand all that you said about your tank installation. I still do not know how you are supporting the center of the plywood floor that is in the middle of the 4' x 5' cavity however. Is the tank itself helping with this?

Also can you tell me where you got the tank?

Thanks,

Malcolm
Good grade plywood would carry the tanks just fine. It does so from the factory in my 71 Tradewind. I am merely duplicating what they did stock on the 71, and also applying it to the grey tank, only with the opening facing rearwards for potential future access. Also, I made minor changes to accomodate the systems as planned for the 1963.
Basically, a frame that is welded on to frame members on three sides, witht eh last side facing rear bolted to the two that are welded to the main frame rails. Now we have a receptacle for a sheet of plywood, on top of which will be the tank.
I have not yet purchased the tanks. I would like to use www.rvpartsoutlet.com for this. They can quote tanks by drawings and do a quick turnaround. Ask for Don. They are in Northern Oregon, I believe.
I have bought quite a bit of general, non Airstream specific stuff there, and always got good prices and excellent service.
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Old 07-21-2004, 01:37 PM   #12
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Plywood support...

Chuck,

My fresh water tank has a groove down the middle that accomodates a beefy about 2" x 2" angle iron cross member down the middle of the tank. The only place on my floor that has a span any greater than 24" center to center is at the very front where there is closer to a 3' span over the spare tire well which is under the floor there. This area would typically be under the couch.

I already have 3/4" treated plywood for all of my floor. If I remove a cross member I would want to re-enforce with something added to my 3/4" plywood rather than having to use alternate plywood.

Uwe,

As it turns out the RV parts store you mention is only about 10 miles from my house. I have been there several times already and agree that they seem to have good prices. I will indeed be buying more things from them. I would be interested in what they quote you for the tank you propose. There are a couple of other sites that I have run across that seem to have a good variety of pre-made sizes. You might check out the following:

http://www.accutanks.com/ronco_holding.htm
http://www.incaplastics.com/rvtanks.htm
http://www.tank-depot.com/dept/69/

Lets continue to compare notes on this process.

Malcolm
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Old 07-21-2004, 02:10 PM   #13
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Quote:
Originally Posted by malconium
Chuck,

My fresh water tank has a groove down the middle that accomodates a beefy about 2" x 2" angle iron cross member down the middle of the tank. The only place on my floor that has a span any greater than 24" center to center is at the very front where there is closer to a 3' span over the spare tire well which is under the floor there. This area would typically be under the couch.

I already have 3/4" treated plywood for all of my floor. If I remove a cross member I would want to re-enforce with something added to my 3/4" plywood rather than having to use alternate plywood.


Malcolm
yup, I'm aware. I'm talking about the "sub-sub floor" that is attached to the bottom of the frame. this is what is holding the tank. I guess if its 1" thick, it can span the 4' and still be strong enough to hold up the water tank...the 3/4 floor that we walk on...maybe its not quite strong enough, hence, AS made the "split" tank, and added that angle-iron support there. Makes me think you could make an exact duplicate of the fresh water tank setup just aft of the axles. of course, you'd have to make new connections, and plug up the old ones, but that could work. The other thing, and I think Uwe already suggested it, would be to use a piece of flat stock instead of the angle iron that would protrude down into the tank space. That may be enough support for the interior floor.

What I'm thinking of doing is making a "half-size" version of that, which would leave the x-members in place...of course, the tank would only be half as big, but I think 24 gallons is a serviceable size grey tank.

here is a crude drawing
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Old 07-21-2004, 02:13 PM   #14
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Malcolm,
Please know that the sources you linked to will not make custom tanks.
Some of the tanks they show look promising, though.
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