When I removed the feed tube to the 3PH I didn't lose more than 8-12 oz. I think, I was ready to catch all 4 gals though.
I put all take off parts up to reuse if I ever needed to replace or return it back to stock so I want to keep them, especially now that I see its about $60 for that tube and the bolts are $7 each.
Dang, parts are not cheap.
You could probably do what your thinking with some fittings and rigid tubing, though I don't think I would plumb everything in hard tubing unless they are mounted to the same thing, I wanted some rubber lines between the tractor and valve for vibration dampening might not be needed I just thought it was a bit safer.