Hi Ruedi,
I would use pvc tubing and leave the tube in the kayak as it is a waterproof hole. Your colour choice but off white or brown look best to me. Sand flush when finished.

: This sounds like a good way of doing it. Just one question: Would I end up
: with the tube in the Kayak or is the idea that I remove the tube once the
: epoxy has hardened? In either case, what kind of tube are we talking
: about? If left in, perhaps a PVC tube? If pulled out, perhaps a flexible
: one?

: Ruedi