Black tank plumbing

[Chuck]

So I'm finally getting moving again on my resto. Got my after market black tank propped in place, and I've engaged a local welder, who is coming next week to make the necessary brackets to mount it to the frame.

after I got the tank propped in place, I'm now having second thoughts.

First, I goofed on the plan, thinking that I can go straight out the side of the trailer with the dump line. I've been looking at the trailer in its present state (belly-pan-less) for so long, I forgot that the main frame rail here is completely obscured by belly pan/banana wrap. The 3" extension that is tacked on to the bottom of the frame is not quite deep enough for a 3 1/2" OD pipe. (I was thinking "3 inch pipe, so that will just fit" doh!).

So in order to keep this setup, I'll have to add another 1.5 or 2" extension to the existing one, so I've got something I can cut a hole in, and also not be so tight to the belly that there'll be room to attach a slinky fitting, etc.

The other thing I'm wondering, after test fitting a scrap of 3" pipe to the tank, is just how much wiggle-room is there with this band clamp attachment? Does the pipe have to be absolutely square to the hole, or can it be bent enough for the pipe to slope down a bit? It will need to go downhill about an inch over a distance of 14".

The original plan was to mirror this extension piece on the curb side so that the whole frame bay could be boxed in with a single flat sheet of belly pan. (longer trailers of the day already had this piece on both sides, and it supported angle-iron cross members that supported a tank pan; The shorter trailers, which had smaller floor-mounted black tanks, only had this extension added to the street side, and it doesn't seem to server any purpose at all.)

Anyway, now I'm starting to have second thoughts about the whole thing. There is plenty of room to just put an elbow into the tank, and run the dump line straight aft to the bumper compartment, then another elbow and go out the side of the frame, as was done with many later-70's models. I just didn't want to consume the limited space there...also, I was thinking (may sound silly) that my "sewer solution" would work better at back-flushing if it had a straight-shot directly into the tank. This might be completely pointless...and really, most plumbing setups I've seen have the black dump that many twists and turns, so almost nobody would have that "feature".

So--should I have the welder add another extension so I can go straight out, or punt and divert the poop to the bumper?