...any DIY
bending would have to be considerably less than even 45 degrees...maybe
even less than 15.

Peggie

Easily less than 15deg bend. Any bends close to that, use a fitting or
two. Dropping a pipe down the inside of the hull and over the "chine"
will almost certainly require fittings.

I was speaking only of the gentle bends that might enable a pipe to
follow fore/aft hull curvature in a small boat. ABS _wants_ to take a
sag or bend, and most pipe you buy will come with a ready-made "banana"
shape. Leaving a pipe suspended horizontally from it's ends with, say, 5
pounds in the middle, will yield a very boat like bend in a week or so.

The major advantage of hose is the ability to snake it through a path
without the need to rip stuff out of the way first; the secondary
advantage is not needing to assemble any fittings. However,
pre-assembled short pieces of piping with the needed bends can often be
installed the same way, as long as you're able to reach both ends and
continue plumbing, when the assembly is in place. You can also
man-handle ABS and bend it quite a bit to get it to go where you want.
If it's going to break in process, it will make a quite noticeable CRACK
that will alert you to your problem.

The disadvantage of hose is that it's relatively permeable and possibly
somewhat less physically tough than hard pipe.

Rufus