Originally Posted by
arex
I read something once, about using linseed oil to coat the inside of the tubes. Being linseed, it would dry into a waterproof coating, instead of just drying out or draining out. It's supposed to be one of those things you'd only need to do once, but it sounds like a huge PITA.
Boiled linseed oil was the standard method of preventing rust in the 4130 tubes on airplane structures for many, many years. Still works better/lasts longer than some modern chemical treatments. I've used LPS-3 in several frames. Also don't generally subject my bikes to water soakings/submergings.