I just installed one of these but I didn't flange the end coming out of the back of the boat.  Will this cause any problems?  I used 5200 to seal it and sanded it even with the transom.

Just curious.  Everything I'm reading says you are required to flange both ends.  Just wondering how this would harm it???

:-?

I guess as long as your silicon don't let loose your good, but I don't think I would want to depend on that.  Look at how big of a hole you're gonna have when you're sitting on the lake and the thing comes out.

I would suggest you try and find somebody that has the tool to flange it or have one made.  

Until you do it correctly, install the drain plug from the inside so no protrusions will be on the exterior to get bumped/snagged/pulled.

Metal or fiberglass?  I wouldn't want water butting up against bare fiberglass... pretty sure it can absorb some water when not coated.. but Im not sure.