A length of pipe isn't gonna get me much volume-- I think that I need to build a rectangular box, using all of the available space, in order to create even 8 gallons worth of "
black tank".
Looking at the entire length from the frame member at the tire, going back until I run into something (a drain valve), and using the entire height to the existing sewage valve handles, I get a maximum size of only:
height: 5" down to the top of the existing valve assembly
length: about 28-1/2" from frame member to drain valve.
width: 13-1/2" from frame member to side of the trailer.
total cubic inches: 1924, not counting width of box walls.
at 231 inches per gallon, that's 8.3 gallons-- about 8, after deducting for the space consumed by ABS walls on all sides. I'll also need metal shielding on the "tire" side, for protection from rocks.
Building a square box is lots more complicated than hanging a length of pipe-- and I'll need to be A+++ with my cementing technique, and glue additional reinforcements along the edges, because it will be shaken during travel.
I can easily craft a metal hanger along the outside edge of the TM, hanging from existing bolt #1 on the frame member which sticks out behind the tire, existing bolt #2 the forward-most of 3 bolts on the frame member which supports the lifting strut.
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It might not be worth the trouble to "shrink" or move to allow for a little bit more space, but what is that box with the ventilation hole and a couple of visible wires behind the ventilation hole screen? Maybe an Output Vent for the fan of the WFCO electric panel?
Any/All Comments will be appreciated!