Correct, The hose would replace the inside of the pipes.
Not as good as replacing the pipes but it's a lot cheaper than digging them up.

Sealing both ends should be fairly straight forward with proper fittings. I'll post any pictures when I get it finished.

Yes, it would be smaller diameter but it wouldnt leak

In my case the smaller diameter hose is an acceptable alternative. If anyone has a better Idea or reason not to try this I'm all ears.