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Old 04-16-2019, 11:46 AM   #1
2 Rivet Member
1968 26' Overlander
Los Gatos , California
Join Date: Oct 2018
Posts: 66
Tank Holding Compartments over the Axels - rear to mid bath conversion

Hello glorious folks of the forums!

I know this has been discussed, even debated, multiple times before on this forum. I know there are people out there who have converted their rear bath layout to a mid bath. There are also many who have wanted to, but decided against it. I believe that I understand the main issues with this project: window, vent, and hatch locations, and blackwater tank relocation.

A mid bathroom is tricky to fit into the window, vent, and hatch layout - which you really don't want to have to change. It seems silly to have a window in the shower (especially when your windows are these pesky 1968 leak-fests). The bathroom cannot be too wide because of running into the ceiling vents. You are potentially rendering an outside door/hatch useless, which you'd like to avoid. A mid bath would also not line up with the ceiling plumbing vent holes from a rear bath layout. Also note that the bathroom now sits on the wheel wells.

Now for the tanks. A mid bath would sit above the axels so one must weld (or I've also seen rivet) a new tank holding compartment to the frame that does not interfere with the axels. Also the drain/valve must be accessible for dumping said black water tank. Many who have done this conversion avoid the black water tank relocation issue by using a composting toilet.

If any of that information is inaccurate or I am missing significant concerns with the rear to mid bath conversion please let me know! Also, I am planning on using a composting toilet but have been told installing a black water system would be highly valuable for resale purposes.

Now for my questions. My 1968 Overlander (originally a rear bath) has a tank compartment in the very rear of the trailer that drops 4-5" below the belly pan. This was originally for the black water tank and no grey water system was in place. My plan is to keep this compartment and have my grey water tank there in the back. It would no longer be directly under the bathroom, but since it just collects shower and sink water (no solid waste) I don't foresee that being an issue (as in, there will still be enough drop in the pipes to let gravity do its work). Does this seem true?

The axels sit below the belly pan. So the order is road, axels, belly pan, trailer frame, subfloor. My frame is 5" tall (bottom of frame to bottom of subfloor). They certainly make tanks narrow enough to fit here (VTS has 4" tanks). So really I should be able to weld or rivet on some metal straps or an entire compartment to hold the tank. My concerns here are 1. future access, 2. insulation, and 3. emptying the tank. First a general plumbing question: must your toilet sit directly on top of the black water tank? I assume it does.

1. Is it super important to be able to access/replace the water tanks (without ripping out the bathroom and subfloor)? Do I need to make a compartment that can open?

2. My original black water tank had about 2" foam insulation around it plus a tube from the furnace to keep it from freezing. I live in California with no plans to camp (at least long term) in any freezing locations. How important is insulation around a black water tank (and a grey water tank while we're at it)?

3. The drain for this tank setup would be located ~1ft away from the side of the trailer, on the other side of the main solid chassis rail and actually in between the wheels. It would be inconvenient for sure to connect the hose to empty the tank - but doable (at least it seems it would be doable to me). What are the concerns with this besides inconvenience? Has anyone come up with a way to make the drain more accessible?

Thank you thank you thank you for your help! I would truly be lost without the forums
1968 Overlander
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Old 05-02-2020, 04:15 PM   #2
1 Rivet Member
1975 31' Sovereign
Federal Way , Washington
Join Date: Apr 2020
Posts: 17
Star Girl,

Just found your thread, I am Mighty Mo, just bought a 1975 31’ Sovereign, completely gutted. Got it home and got the body off the frame to get work done on it. My daughter and I are collaborating on this project. We definitely want to go with the side bathroom and make the rear a bedroom. I’ve been combing the airforums and internet in general for a plan to relocate and build a support system for the various tanks. Like you we have considered a compost toilet and at least one person has said keepi a small black tank for urine only, so you only deal with solids. It also makes one consider how to maximize fresh water tanks and accompanying gray tanks. So far I figure to replace the fresh water tank with a new similar one because it has a lot of nasty debris in it. Seems difficult to find ori fabricate a way for a bigger one than the current 45 gallon. But I’d like to move the gray water tank forward more to relieve weight in the back, and possibly have a smaller black tank for Liquid wastes. But you have one chance to do it right with a frame off situation so maybe I should put a full size black tank that if desired could be switched back from compost to flush toilet. Hard decisions.
Wondering if you ever finished and what I might learn from your conversion. Particularly I’d like help on how you build a support system to hold the tanks and how you plan for the hole to empty it. You can see pictures of my frame at Mighty Mo.
my name is Mike, I’m in Seattle area. Thanks, hope to seei your finished product
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Old 05-02-2020, 11:29 PM   #3
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1958 26' Overlander
Battle Ground , Washington
Join Date: Jun 2013
Posts: 543
Images: 22

You have an alternative on the toilet/black water tank locations if you go to a macerating toilet. It does not require you to mount directly above the BW tank. I have a Raritan model, which has a side discard line so you have some freedom in routing the drain line to your BW tank. It does add complexity as it requires an electrical circuit to run the motor (mine requires a 25 amp circuit). Mine also requires a pressurized water line lead for flushing and you'll want a P trap shape in the discharge line for odors.

Far from simple, and most people don't like the complexity. Just letting you know about an alternative.

Question 1 - Access needs to be from the bottom.

Question 2 - I see no reason to insulate with your reasoning.

Question 3 - I don't think you'll want your discharge between the wheels. Increases the chance of damage from debris coming off the tires.

Suggest you add photos when possible. Easier to understand the issues your trying to solve.
Harold & Rebecca

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Old 05-18-2020, 09:40 PM   #4
2 Rivet Member
1968 26' Overlander
Los Gatos , California
Join Date: Oct 2018
Posts: 66
Hi! I had given this thread up for dead I'm glad it's seeing some action.

Mike - I am very much still in the middle of my project and have not even gotten around to decisions that affect bathroom location. I am planning on the mid bath and I am planning on getting some sort of black water tank in there even if I end up with a composting toilet. This blog has been helpful for the tank support/location (and lots more!):

Here are some photos for reference of my (planned) layout:
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1968 Overlander
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Old 07-16-2020, 01:00 PM   #5
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1975 Argosy 26
1979 30' Argosy
Join Date: Jun 2011
Posts: 459
Any progress on your question & ideas? I already have a center bath but want to move the above floor black tank to the frame so Iím interested in how you decided to proceed.
1979 Argosy 30
2001 Ford Excursion 7.3L
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Old 07-16-2020, 01:40 PM   #6
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1966 22' Safari
1955 22' Flying Cloud
Fredericksburg , Texas
Join Date: May 2015
Posts: 1,583
If you place the black tank between the axle, I assume the outlet will be on the streetside? Consider a bit of slope for the tank. Good luck
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Old 07-16-2020, 09:04 PM   #7
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1972 31' Sovereign
Silverton , Oregon
Join Date: Aug 2014
Posts: 286
Images: 48
I made room for a largish gray tank with a lift and located it near the rear axle, there's room for another in front other than the shower drain.

with a welder and a laser cutter nearby crossmember's can be made and welded in.
"Daddy when's the trailer going to be finished?"
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