Black Tank in Cargo Trailer

[Zork]

I've been going back and forth on the idea of adding a black tank to my cargo trailer conversion.  The main reason for adding one would be for versatility - it would let me use LTVAs and campgrounds that require such a tank.  I'd rather just use a composting toilet, etc, but if the downsides of installing a black tank aren't too bad, I'd like to add one during the original build.

Thing is, I don't understand how they are mounted.  My trailer floor cross-members are 16 inch on center.  And I don't want to decrease clearance under the trailer too much.  Are these typically mounted underneath, along the frame of the trailer?  Would mounting them on a raised floor for a toilet/shower be a reasonable way to avoid the clearance issue underneath?  I'll add some photos of a couple I found.  The minimum required volume looks to be 10 gallons (per BLM, at least).  These are 10 and 14 gallons and would seem to fit between my 16" on center cross-members since they are 13.78" and 14.5" wide, respectively.  Appreciate any thoughts on this, thanks.

 

[Zork]

sorry for the picture size, but hopefully you get the idea. Maybe I can edit the size.

 

[Zork]

one more - not sure how the "wings" or "rails" are used for mounting.  I've seen some tanks with a 1/4" thick lip designed to drop-in through the floor, but none of those tanks are small enough to fit my floor cross-members.

 

[Zork]

one more - not sure how the "wings" or "rails" are used for mounting.  I've seen some tanks with a 1/4" thick lip designed to drop-in through the floor, but none of those tanks are small enough to fit my floor cross-members.

an example, but too wide:

 

[B and C]

My tanks are held up with metal C channel cross wise and threaded rod up to the support. Mine are on a Roadtrek for reference.

 

[Zork]

Thanks, Brian. That helps. I need to get out and look at some installations in various vehicles to get some perspective.

 

[maki2]

Some of the professional conversion van companies put in one of the Dometic All-in-One toilet units that are come with an attached tank. You would need a space to install it. They often partition off the rear of the van for a toilet/shower/storage room. You might possibly find a used one from an RV salvage yard or from an auto parts salvage yard if your funds are tight. The advantage is you don't need to put a black water tank underneath the van so the installation is pretty darned quick.
Dometic 711-M28 All-In-One Toilet System

This website has below average pricing on the unit.
https://www.defender.com/product.jsp?id=105225

Link to the owner's manual. https://www.defender.com/pdf/500258_OwnersManual.pdf
Note that you will need to add a vent up on the roof or in the sidewall above the height of the tank. All black and grey water tanks require venting to keep the pressure equalized so waste can go into and then be drained back out of them and also for odor control. You want the vent to be located away from a window or rooftop fresh air vent so that you don't get the odor pushed or pulled back into your van.

This toilet/tank and a grey water tank under the sink that is equipped with a vent and drain port will qualify you as being self contained for the LTVA regulations.

 

[Zork]

Hi Maki. Thanks for that information. I noticed that the tank size (9.5 gallons) falls just below the minimum (10) required by BLM for some LTVAs. I think that if I go for such a system, I'd want it to clearly meet the letter of the law. But this gives me some other ideas, and I appreciate the reminder regarding venting.

 

[tx2sturgis]

If you mount a holding tank of any kind UNDER the cargo trailer floor, you will greatly reduce ground clearance, AND you will likely have issues when the temps go below freezing for any length of time where you are. There is no guarantee you can always avoid freezing temps (in the USA) all the time, even in the desert southwest. Balance and weight distribution also has to be worked out, since there will not likely be room to mount it under the floor AND over the axle. 

Much better to find one that can mount inside, maybe over (or just ahead of) the axle, with the toilet drain (and maybe sink drain) plumbed in such a way that gravity will work for you, and of course, venting and outside dump capability.

Keep in mind that the rangers will ask about it at the LTVA, but they will not inspect it to make sure you are filling it from day to day. You can, of course, figure out how to minimize use of it, OR you can use a portable blue-boy to effect waste dumps without breaking camp.

 

[Zork]

Thank you, tx2sturgis. You have given me many thoughts to ponder.