Was trying to find a photo showing your concerns with the sewer line connection concerns without any luck...
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I'm guessing it must come out near the rear of the trailer.
The sewer lines can always be changed if that turns out to be a problem... I would think as long as you know of any close proximately thing when backing it really shouldn't be an issue. i.e. you will be aware of the possible backing hazard.
Looking at all the interior photos of this trailer on-line it certainly looks like a real nice layout inside for you.
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photos from google images
Roy Ken