Teardrops n Tiny Travel Trailers

hello all;
i appologize if this has been answered previously but i cannot seem to find the answers.

i plan to mount a residential style toilet in my cargo trailer conversion.
my joists are 16" on center.
my delima's:

i cant seem to find a very good selection of black water tanks narrow enough to
fit between 16" joist span; so that i may mount the tank flush up aginst the bottom of
the 3/4" plywood floor. if I use a larger tank:
is it typical for the black tank to be mounted flush with the BOTTOM of the
JOISTS as opposed to the bottom of the plywood?
if acceptable then:
how specifically would i plumb from the bottom of the toilet, through 3/4"
floor, span the 3" of joist height "void area", and finally into the black tank (this connection
would be in free air, with no lateral support- if that has any bearing...)

it also seems that sufficient bracing for the tank itself would be difficult- in order to
eliminate any shifting- especially during a heavy breaking situation.

If you can find an old truck camper that is scrapped, you may be able to find a 15" W x 6'L tank. I got the gray water and blackwater tanks out of an old 1995 Fleetwood Elkhorn truck camper. They are about 25 gallons each. Perfect fit between 16 inches on center floor joists.

Alternatively, there are place that will make to order any size you want.

Sent from my SM-N970U using Tapatalk

Biggest issue is dealing with 'solids'. My plan is to do a Wag-Bag (semi compost) style to deal with the solids. Mostly we find other places to poo, but there's that time when you just have to. Dealing with just liquids, then an easy mix with gray water and only a tank required.

I'm hoping to use carboys and adapt a fitting. Something like this (probably 2): https://www.uline.com/Product/Detail/S-12768/Jugs/Carboy-5-Gallon

For my fresh water something like this (will probably buy 4): https://www.uline.com/Product/Detail/S-15648/Jugs/Carboy-2-1-2-Gallon

The actual RV ones I've found run $160-$260 and still require piping and dump fittings..

In California, what causes a trailer to be classified as an RV and not a utility trailer is whether it has a plumbed toilet in it; so, you might want to check the state you live in to see how it's handled there. The registration rules and costs might be a bigger deal on an RV and that might be worth considering.

Thank you all with this good information. I will consider all of these!